Surely you remember trade offers in fifa 14 and part of 15 and any fifa before then, right? They were sadly removed, as we know, to stop coin selling. Well here's a way you could bring it back in, EA. (Warning, it's complicated, so read slowly and make sure you understand before slating it)
Every player has a price range. Take the median of that price range (the middle number) and have that as the player value. Eg:
350-10000 = 5175
Every trade offer needs to be with 2 values of players and coins that are within 25% of each other.
5175 player <-> 10000 coins? NO
50000 player <-> 30000 player and 10000 coins? YES
This means that the values of the items being traded would be similar, and so no cheating or scamming