Reply to CDJ-850 CD reading tolerance

Can anyone who's had an 850 or similar for a good amount of time answer this? I've had a preowned 850 for about 6 months and has been working great, especially since have been using mostly USB. I had a performer hand mea performance cd during an event andbecause of the time didnt cue it like I usually do. I skiped pretty bad during the perfomance. I pull out the cd and look at it,, little to no scratches but a nice sized thumb smudge fingerprint, MY QUESTION : Should the cdj freeze up on this or play through it? is this normal? Or is my CDJ failing? Maybe I should crarry a cloth around or something... Thanks in advance