You should read the post before commenting. They're not selling any games anymore, they're open sourcing everything. So how would it affect sales? And yes, you

You should read the post before commenting. They're not selling any games anymore, they're open sourcing everything. So how would it affect sales? And yes, you can, but if you take their code, fix it or whatever and then sell it you will still have to provide the modified code under GPL since the original was licensed to you under GPL. But as long as you do that you _can_ charge for the distributable of course.