I would agree that you should verify that the bids you receive are comparing "apples to apples" when comparing bids. In another profession, it was typical for contractors to "lowball" their bids and then make up the money on change orders. Sometimes the contract ended up costing more than twice the original bid price.
i'm not an expert, but I do suggest looking up any contractor on services like the BBB, Angies List, and the State of Michigan website. You might also want to verify they have valid insurance and bonding.
I agree with Keith. It is best to prepare your own itemized list (before or after you talk to 1 contractor); then you can use the list in communicating with another contractor(s) to make sure you all are 'on the same page'.
Sometimes, it is very difficult to do if you are not experienced or don't really understand what is involved, since the contractors will give a different level of details on their proposal (and that could be a huge area for $ and expected quality difference). It helps when you are open about talking to other contractors and tell each that you expect another quote with a good breakdown labor and materials and that you will make your decision whom to chose after that. A good contractor does not mind a little competition, an honest contractor will respect your honesty and try to be as thorough in his estimates as he can, a bad contractor could disappear w/o giving you a quote.
If you trust the person who gave you a referral you should still do your own homework and check out 1 more. There is a good Russian saying "Trust, but verify". Good luck!