Get it in writing

If you make an agreement — big or small — write it down and sign it. No matter who you are dealing with, an unsigned, unenforceable promise is worthless. And if the other party will verbally commit, but will not sign, let that be a message, too.

For trivial matters, you do not need a lawyer or a template contract from the internet. Just write down what you are agreeing to in plain English; for a simple deal, a few sentences will suffice. Be sure to spell out contingencies, should things not work as planned.

When there is a considerable amount at stake, seek competent counsel.