What kind of relation about the salary to the transfer prices?
a type of player who is selled for a high price, get a high salary and a player who got selled cheap a low one - because transfer prices are the best indicator of demand in this game and demand is usually the key who is also considered for the salary negotiations.
In this scenario, you wouldn't pay less for a center, who have 10 additional insideskills, because he is more useful then the guy with 10 less skills ;)
But for this you need working tpe, so that players who get trained, get a updatet value from time to time.