Do you need to know if the title is clear? Do you have that as a contingency in your offer to buy contract?

[Linda Pierce]

I am educating myself like crazy right now. I plan to begin my business wholesaling houses. I am currently watching Steve Cooks wholesale DVDs that he did in Long Island a while back. But I don't quite understand about Titles. I know he recommends finding a good title company with experience. But my question is about when you are making an offer to buy. He emphasizes not using "Weasel Clauses". I understand that part. When I went online to find sample offer contract forms, one included a clause that the seller must provide proof of marketable title. Is this necessary? If the title company finds out there is a lien or something, am I still obligated by the contract if I have not added this clause? Thank you all for any responses.
Linda