It would make people jump if the Library checked the returned items and charged if not in good condition. After all they know how many times the goods have been taken out of the library in the first place. Maybe a deposit should be levied based on return in good condition.
Unless the original fee and the number of times used equals the value. Popular loans would pay for themselves in wear and tear.
It is then a case that the library should not issue a faulty dvd/cd.
Take them back and if possible tell them where the fault(s) are. The Library should check your findings and reimbyr you or offer another rental. If you just say they are faulty then someone has to play them all to find the faults.
A lot of people have no respect for other people or their property.
I used to work in a video library and you should have seen the state of the tapes people returned, they were often covered in food, juice, grease and other unsavoury substances. If the tape was not salvageable we had a nice man who went round to the customers house with the tape and an invoice for a new copy, people rarely refused to pay when the alternative was great pain.
Also my wife worked in a library during her student days and there were some interesting things used as bookmarks, and no kidding she once got a book returned with a rasher of bacon (raw) neatly tooked in the back pages. Unfortunately libraries rarely have access to the type of man who used to recover my employers costs...