The best offer I have ever received was almost 20 tokens. It's more than half of the tokens I received in whole season. At that time I might not even seen a 4 token offer before. I thought that the offering manager wanted to give out all his remaining tokens and would quit. Even though the player was best striker of my team, I decided to accept the offer without hesitation.
The buyer need to spend another token to change name of the player if he don't want to receive many offers for his new player. BTW, it is quite usual that new owner will immediately receive a new offer on the player from another manager.