Post-make contamination is not common unless there are aging room issues with listeria or pathogens. Slip skin can be eaten, though it may not be the most appetizing. It's more common to find contamination due to poor cleaning in the holding tank, or equipment.
Best signs are a smelly (putrid) or "off" cheese. Most molds, yeasts, and bacteria that cause spoilage are not deadly. Unfortunately, there's no sure way to tell without culturing and testing.