Hi
Negotiations work by making offers for players using tokens and you can offer some tokens to a seller to help them consider your bid, however the more tokens you offer then the more it will cost you and it would be worth just buying a scout.
Players rated 5* close to 6* are on your list and each as an initial token bid which you must pay minimum to make an offer,
Just say the player you want to buy costs 7T and you want offer the seller 5T, then it will cost you 17T tokens to offer because for every token you offer you need to pay another token in commission. You can offer anything upto 20T but that could mean your paying close to 50T which is a cost of a scout player.
Selling is where Negotiations can become useful, when you are selling players and want to have a chance of recieving a bid via negotiations then you need to train your player 1 or 2 skill points short of getting the next star and don't apply any more skill points earned in training, this allows your player to be listed on the Negotiations list for a while, othe players can make an offer and if it involves receiving some tokens you can accept this, it beats placing them on auction as you wouldn't get any tokens.