Is it OK to make changes to GPL products and then charge for them? It says Who would 'third parties' be? The original creators of the product? And is it correct that when selling a GPL product, any person who buys the product can then sell it themselves under the license?
Here's what is said in the FAQ... http://www.gnu.org/licenses/gpl-faq.html#TOCTheGPLSaysModifiedVersions
What it is saying is that: First Part 1) you can charge a delivery fee (download fee, shipping fee, etc.) 2) You can charge to provide a warranty or to provide support. Second Part 1) if you create a program based on or containing the software you must a) make your derived software available under the terms of the GPL - of which the highlights are a) make your source code available, and b) you can't charge for it, but c) you can charge a delivery fee or a support fee, although d) anybody who you give the software to is free to distribute it, again, under the terms of the GPL.
Looking at http://www.gnu.org/ the selling FAQ looks like it's encouraged!!! Bill Gates, interested in buying some hacked CMS scripts??!! My idea is geting CMS programs that don't have search engine friendly URLs (Or improve on ones that do.), change the script/mod-rewrite them and then for $49.95 let users have access to all of them including future updates, and the source code, which tells what was changed, search and replace code. I thought so. Though out of 175 users of another GNU/GPL product I sell, I have yet to see any one sell the same thing.
Lots of people already do this. Look at Red Hat Enterprise or any Linux distribution for that matter. Yes you can download them off the web but you can also pay to get the CD. The only condition to distributing GPL'd software is that you provide access to he source code.