Since you can't control the way the customer treats the disks or the fact they have a cheap disk if it is a copy then you will have those problems. I have even had customers bring me a cracked disk and told me it works on their player at home.
Try inspecting and cleaning their disk for them before you attempt to import from it. If the disk looks too scratched or damaged then I would tell them (politely) that you can't load it and show them why. Explain to them the proper care and feeding procedures for CDs.