They are actually not fabricated, but rather calculated by the most reliable source of the kind (transfermarkt.de), that being said, it doesn't tell you shit about the ability of the player in question, because it also takes into account the players age, time remaining on his contract, and the like.

So you can't just go "zomg that guy's 55 million good, and that other dude is only 25 million good!" - because older players tend to be cheaper, and being on the last year of your contract also takes a dump all over your market value.

Edit: The value of your last transfer also factors in.

Casciavit wrote:Goetze>>>

This.
Götze has been absolutely amazing since his return from injury.

The point is, it's been made up using a number of random factors.

A player is worth what the Market deems them to be worth. Using prices to compare players proves absolutely nothing.

Transfermarkt fees are a result of random users making those numbers up in the Transfermarkt forums. Pretty much as if GL opened a "value players from team x" thread in the respective sub-forums. In other words: completely useless. Especially given that the Transfermarkt community is like 15 years old on average.