There are plenty of things you need to be aware of, but most importantly, you need to ensure that the contract does not contravene any trade practices or consumer laws, otherwise your contract will be deemed void if it were challenged in a court of law. This is something you need to get checked out with a lawyer.
I don't live in the U.S, so i'm not familiar with your trade practices or consumer laws, however, here in Australia they are very strict and it becomes tricky when trying to write a contract that is tight enough to protect yor own interests, while at the same time ensuring that in doing so, you don't contravene any trade practices or consumer laws.