Whenever we make a deal with someone, whether it is for us to buy something, sell something, or just agree upon working together in some way, there is a tacit assumption of trust in the relationship.
While we may have contracts, sales agreements, and all sorts of documentation to enforce a certain expected behavior, unless there is an intention to truly fulfill what you both agreed on, and trust that it will happen, nothing will move.
While contracts are helpful for taking someone to court, if the person was out to get you from the start, they most likely thought of a way to get out of whatever responsibility they may have agreed to.
So how do you do business at all? You have to know yourself, trust your judgement, and listen to that little voice inside that intuitively knows whether this is good for you or not. As you learn to trust your intuition, exercise it, rely on it, and recognize when it is real or just wishful thinking, it will be your best protection against making a bad deal, with anyone!