Can I sue for breach of verbal contract?

Most types of contracts do not have to be in writing, and the type you're describing sounds like one of them.  Thus, if you had a verbal agreement to be paid a sum of money for typing someone's Master's thesis, and they didn't pay you after you had performed the agreed services (typing), you would have a valid claim for breach of contract.  However, if you truly agreed to help someone cheat by writing their Master's thesis for them, it is likely that such an agreement would be deemed void for being against public policy.