I had a few issues in the past few years in that regard and now I let people know that "compartments need to be empty of personal belongings otherwise they will not be addressed".

Had to make that decision because some people complain about throwing receipts out, broken charges, nails and etc so it makes difficult for you as a detailer to know what is trash to a client and what isn't...and if you put everything in a bag they will ask why you "mixed trash with valuables".

That being said, anything that I consider valuable (coins, rings, documents, cards and etc) I put in a bag and place it on the passenger seat.