Why do players values differ?

On manager mode I have a few of these.

I have two CBs that I've developed up to 82OVR. I keep getting offers of 20m for one and the transfer bloke says I can push for 35m. The other one I barely get 10m offers and the bloke says push for 18-20m.

I also have a winger who is 86OVR and his value is 14.5 mill and people won't even offer 20m.

Da fuck?

Length of contracts, age, form.

I signed them both at the same time on the same contract. They're both around 20.

I do same thing over and over. Buy players aged 18-21 with around 77-79 OVR. Let them develop to 82+ then sell to Madrid for 30-40.

I did that with 2 of my strikers. I got a random one like that, he got to 82 and I sold to Madrid. They offered 20m, I said 40 for shits and giggles and they said yes.

Bought Luc Castaignos, got to 82. Madrid would only offer like 35 but I took it.

Now I've got a striker but his value won't get near that mark and his OVR is 86.

Its fucked up.

Different potential. All the players have a set potential in the game that they will definitely reach. So if you have two 80 rated players and one is much more expensive than the other then it could be because one's set potential is 88 whereas the other's is 84.