Some concessions purchase trust more effectively than money.

Some things you can give are worth more as signals than as substance. Volunteering information that helps them, conceding a point before being asked, holding to a term that has become inconvenient for you, all of these tell the other side what kind of counterparty they have. That knowledge changes the rest of the negotiation and often the next one. It is cheaper than the equivalent in price.

Look for one concession you can make early that demonstrates good faith rather than weakness. Say plainly why you are making it. The return usually arrives in places you did not specify.