Normally I take 0 tokens as an offer on the negotiation table, so it enables the seller to put an acceptable set price to sell to see how much they think hes worth to their team.

I sometimes give 0 tokens negotiation offers just so I can then see the set price so I can decide whether to buy him outright. Obviously sometimes this message doesn't go through.. If I get an instant rejection I consider it a player that is not for sale.