getting paid

[Ivers, Doug E]

I'm still in a learning mode, but in the not too distant future I want to
write stacks and sell them online for a few bucks.  What is a good strategy
for locking out users who haven't paid the fee?  This goes beyond
password-protecting scripts.  It involves setting up a registration code
system so that each user ends up with a different unlocking code.  While the
stack can be downloaded by anyone, it won't run without the code.  In some
cases, I may allow free access for a period of time, and then the code is
required for further use.

I've never done this in any programming language.  Any advice?


-- D