Is a contract legal if it's not filled in all the way, and things are left blank, and then added after you've signed?

A roofer got us and some neighbors to sign a contract for him to talk to our insurance agent and show them roof damages. He said the contract was for him to talk to the insurance co. then he tried to go back and fill in an amount after days of the contract being signed. The contract we have has no price on it, because he left that part and other parts on the contract blank. Can we use another roofer and not be sued, he's wanted in three states and is an illegal immigrant, we don't want to use this thief, his story is on the local news.