I'm just assuming that what ever you've built, it has CPAN modules in it. You're really going to have to do your homework if you want to sell a product that's reliant on CPAN modules (ie, you may have to negotiate a separate license from the module creator - if you can find him/her). *Or* you would have to package your application in such a way that part of it is *free* and part of it is not.

IANAL, but I think all CPAN modules that are distributed under the "same terms as perl itself" can be used without problem in closed source, commercial applications. Just the like the core modules that come with perl itself.

This might not apply to GPL-only modules. If you use a module, one might argue that it's the same as with linking against a GPL'ed library, in which case the whole application must be GPL'ed.