Although domestic airline tickets are more volatile [ie, prices change more frequently], the price difference between major travel sites [such as Orbitz, Travelocity, Expedia] and airline sites typically does not exceed 10-20%. Domestic air ticket sellers fall into two broad categories:  airlines and  online travel agencies. There are some niche markets, but they serve a small market. Therefore, when purchasing a domestic ticket, “when to buy” is usually more important than “where to buy”.
The opposite is true when securing international ticket transactions. “When to buy” is still important [for example, don’t wait until the last minute], but “where to buy” is even more important. This is because airline tickets to Europe, Asia, Africa, and Central and South America are less volatile [may change less frequently], but price differences between different suppliers can sometimes be as high as 50% or higher. There are several reasons for this, but the two main reasons are:  the type of fare provided; and  the number of people on the scene.
In the absence of very skilled technology, there are basically two international tickets; published and unreleased. In the domestic market, 97% of leisure fares are made public [given or accepted]. You can refer to a published fare as a retail fare. The airline creates fares and rules related to the fare, and then publishes the information through a clearinghouse called ATPCo [Airline Tariff Distribution]. ATPCo then assigns the fare to the global distribution system. Online and offline travel agencies retrieve these published fares in turn through one or more systems. Tickets are available to everyone. The unpublished fares [also known as negotiated fares] are still being released through ATPCo, but part of the "Fare Rules" indicates which fares are allowed to be used and sold by the seller. It is essentially a private fare. Another difference is that the published fare must be sold at a price determined by the airline [no increase or reduction], and the fare can be increased. That's why you'll see the online and offline agents add a service fee between $5 and $50 to the published fare. By negotiating the fare, the airline will receive a fixed amount and allow the seller to increase the fare [increase its margin]. Therefore, the seller can negotiate with X Airlines for a $300 fare from New York to London, then increase the price and sell it for $345. Another significant difference between negotiated fares and published fares is that for many [almost all] negotiated tickets, you will not see the actual price of the ticket. Instead, you will see higher fares or only tax information. The published fare ticket will accurately show the cost you paid for the ticket [not including any service charges]. Usually, negotiated fares are usually cheaper than published fares [in some cases, airlines may conduct “big sale”, which weakens the fare level of negotiated fares], so “where” is better than Where is more important when buying an international ticket is "when."
Sellers of international air tickets are divided into the following main categories:
 Major airlines
 Charter airlines
 Online travel agency
 Offline travel agency
 Global integrators sold to the public
 Global integrators not sold to the public
 Ethnic integrators or destination experts
 Student travel merger
 Travel agency
These are carriers we are familiar with, such as American Airlines, United Airlines, Delta Air Lines, Northwest Airlines, Lufthansa, British Airways, and KLM. They offer tickets through their own website and many other sellers listed above. They may offer special offers on their website. They do not charge a service fee.
In Europe, this type of airline is more common than in the United States. Basically, chartering is carried out when a travel agent "rents" or "charters" aircraft takes vacationers from their departure port airport to the destination airport. Several airlines that provide services in/from the United States originate from charter flights. They regularly offer year-round or seasonal services from select US airports to individual countries. They have been approved by the Federal Aviation Administration [FAA] and must comply with all aviation safety rules and regulations. What sets them apart is their business model, which allows them to sell seats cheaper than professionals. Some of these alternative airlines are LTU, Condor, FlyGlobespan or Martinair. They usually do not charge a service fee.
Online travel agency
The players in this category are Travelocity, Orbitz, Cheaptickets, Expedia, Priceline, Hotwire, etc. They sell both issued and unissued tickets. They charge a service fee. They also habitually sell other travel ingredients to you, such as hotel accommodation, car rentals, attraction tickets and/or travel insurance. If you want to buy a package abroad [the seller bundles the aerospace component with one or more land components] is an option and can save you money. In future articles, I will introduce the advantages and disadvantages of the software package.
Offline travel agency
Also known as physical travel agencies, these are traditional travel agencies where you can enter, sit down and book trips. Depending on the size and target market, they may also serve as racial merging or destination experts. They can also use comprehensive fares that are not directly available to the public. Entity companies almost always charge a service fee.
Global integrators selling directly to the public
Many of these travel agencies have decided to "cut down the middleman" and go directly to the airlines to negotiate their own private fares. In this way, they can resell them at a lower price without losing their profits. In order to obtain decent private fares, global integrators must provide more than $100 million in agency sales revenue each year. Most of the negotiated tickets are sold for free. If the merger sells the public fare, they will periodically increase the service fee.
Global integrators not directly sold to the public
In the days before online Internet travel, few agents acted as their own integrators. Instead, they work through middlemen [integrators] who negotiate deals with airlines. The merger will negotiate the same $300 transaction above, increase his margin, and then sell it to the retail agent. The retail agent will then increase its margin and sell it to the public. With the formation of the Internet, agencies can attract more audiences and therefore have the influence of negotiating directly with airlines. However, there are still many organizations [both offline and online] that offer middleman integration services. Since the combined company can provide a large number of airlines, even if the price is increased several times, these fares may still be cheap.
National integrator or destination expert
These may be one of the [most least known] sources of cheap airfare. They are also the hardest to find. The United States is an immigrant country, and ethnic consolidators traditionally serve their former patriots or immigrant communities. They used to be and are still cheap flights for return tickets. Unlike global mergers that can generate more than $250 million in annual sales, these ethnic outlets may only generate between $2 and $5 million a year, but most of them can be handed over to one or two airlines. They are highly specialized and have a long-term relationship with their favorite carriers. These long-term, reliable relationships are the reason why certain ethnic moms and pop musicians can ensure that ticket prices are 20% to 30% lower than any online large agent. In terms of size and style, the destination commissioner is similar to the race merger. They have become true experts in a country or region and have established contacts. The difference is that they are usually targeted at foreign independent travelers [FIT]. As I mentioned, some of the offers that airlines can offer are often difficult to beat, but finding them is a challenge. Google and Yahoo and any other search engine usually can't find them.
Student travel integrator
As the name suggests, these institutions are aimed at students [in some cases, teachers]. Like global integrators, they approach airlines and negotiate special discounts or private fares. The difference is that, according to agreements with airlines, they are only allowed to sell to real students [and faculty]. Usually, students must enroll in an accredited college or university, while high school students are not eligible. The same is true for teachers. Some intermediaries are better than others in ensuring that the people who purchase tickets are actually students.
A tour operator is an entity that sells vacation packages [such as all-inclusive]. They negotiate deals with airlines, hotels, ground operators, etc., package them together, mark the price, and then sell it as a product to the public. Sometimes they only sell tickets [sold at the lowest price] to fill the empty seats on the plane. Since they have to pay the aircraft operator for a fixed price, any empty seats are missed opportunities. The best chance to get one of these cheap seats is usually to travel to the Caribbean or Mexico.
There are many sources of international airfare transactions. Finding the right person at the right time can affect everything you get high or low. Although getting a domestic ticket transaction is usually the result of a [lucky] timing, getting a huge international deal is usually the result of knowing where to look.