I'd say that sellers has very little incentive to sell players this way.
Because of the high commission, they see very little of the tokens paid.

According to me Nordeus caused the problem via two mistakes
1) They devalued cash in the game with the high competition prizes and recently with the daily giveaways. Cash is worth nothing except at low levels
2) They raised expectations by letting sellers get tokens in negotiation. People are not stupid, they know how much they pay in tokens when they buy, and feel ripped-off when receiving only a fraction of it when selling.

A possible way to fix it with compromising their revenue it could be as follows
- make cash scarce again.
- make buying players cost mostly tokens
- make selling players bring only cash

For the buyer, well, seen the prices on the auction market, negotiations can be interesting if you don't want to wait for the right player to show up on one of the 360 daily auctions. It's a fine line. You can't make the player too cheap for the buyer otherwise you kill your auction market.