all depends of the coach,,, I did a good offer for a 2* player of a team + 3 levels... (yeah, the player had 5* for me)... he did not accept, and... really I don't know why... because he have a team of 6-7* for his level...
Now he sold this player for less money in market... so... don't try to understand other managers...
Usually, if a player have quality in his team, for example, a player of negotiations list, of my level, I do an offer of the value +50%, if I realy want this player.
If in his team the player have 2*-3* less... but... you never know...