A Proposal/Estimate is the most important form a freelancer must put together.
You should be able to specify your terms to avoid needless pain. If the client hands you a contract, you have the right to amend it if you consider it unfavorable to you.
If you accept unfair terms because you need the money, at least make sure to add the following line:
"I hereby reserve the right to tell you to Go Fuck Yourself"