I had very few clients who were not, and had been relieved that was the case.  I've had a few cases, where the uncircumsized penis would overly leak, a faint smell, and also have noticed that they were not overly clean.  I won't say that this was all of the cases that I have seen, but it was the majority, that I have met while providing. In those cases, I would make sure that he would put the rubber on, while oral was going to be performed.