Did you set up any conditions to the loan before they accepted it, such as "I will loan this to you if you promise to return it in similar condition or pay X$ if its lost or busted". If you did not, then you should not set conditions now, its to late. If you find fault now, your second guessing, and its really your fault for not being up front with what you expected from them.

It hurts, accept this as a learning experience, and move on. Good Luck. JMHO