PrestaShop License : GNU GPL v3
GNU GPL FAQ : http://www.gnu.org/licenses/gpl-faq.html#DoesTheGPLAllowMoney
Does the GPL allow me to sell copies of the program for money?
Yes, the GPL allows everyone to do this. The right to sell copies is part of the definition of free software. Except in one special situation, there is no limit on what price you can charge. (The one exception is the required written offer to provide source code that must accompany binary-only release.)
Quote : “Many people believe that the spirit of the GNU project is that you should not charge money for distributing copies of software, or that you should charge as little as possible — just enough to cover the cost.
Actually we encourage people who redistribute free software to charge as much as they wish or can. If this seems surprising to you, please read on…. http://www.gnu.org/philosophy/selling.html “
So, in my understanding, there’s absolutely no wrong to sell/charge a fee on customized themes. You spend times and skills to create themes so you deserve to be appreciated.
Business on sub forum ??? IMHO, it’s more like an OFFER just like Prestashop team who creates PrestaShop where they aren’t obliged you to accept it nor refuse it but they give you a way to appreciate them such “Donate”.
If it’s not on the forum, where else ?
Peace !!!