If it were me, I would simply look for and adopt someone else’s license enforcement mechanism, and leave it at that.   I do, in fact, sell a commercial product (tho’ not in Perl), and my experience has been that you can spend just as much time as you care to spend, imagining how everyone on the planet must, surely, be stealing copies of your stuff (and going to very great lengths to do so).   “Did it ever occur to you that maybe the reason why people aren’t buying it is because your product sucks?”   :-}   You are quite likely to lose customers and prospects if you make your mechanism obnoxious.   (For example, I have a standing rule:   “No dongles, or No Sale.   No exceptions.”)

The most important aspect of a serial-number control mechanism is simply that, “it exists.”   I vividly remember how a friend of mine kept an expensive guitar in a cardboard case secured by the tiniest padlock imaginable.   It was, he said, “to keep the honest people out.”

I have also been told that some purchasing departments, especially of governments, are not allowed to pay (public) money for something if its benefits can be obtained without a per-unit purchase... hence, there had to be some kind of a serial number, “something that must be bought.”   I always thought this sentiment sounded rather peculiar, so don’t quote me on it.

Your Mileage May Vary.™