WARNING. Everything other than the last paragraph is kind of rude and opinionated, so skip to the bottom if you only want practical advice and not a philosophical rant.
First of all Free Software don't need paid developers. We scruffy hackers create software because it's fun. I have a strong suspicion that the commercialization of Free Software via the businessfriendly clothing "Open Source" is actually creating a lot of shitty software or at least a lot of good software that'll be obsoleted to keep business going. Capitalization of Free Software doesn't have an incentive to create good finished software, quite the opposite. The best open source software from commercial entities is in my opinion those that were open sourced when a product was no longer profitable as a proprietary business. As examples I love the ID software game engines and Blender. Others seem happy that Sun dumped the source code of Star Office, which then became OpenOffice and LibreOffice, but then again companies like Collabora are trying to turn it into a shitty webification instead of implementing real collaborative features into the software like what AbiWord has.
..and back in the real world where you need to buy food. Open Source consultancy, implementation of custom out-of-tree features, support, courses and training, EOL maintainance or products that leaverage Open Source software is my best answer. See Free Software as a commons we all contribute to, so that we can do things with it and built things from it. You should not expect people to pay for Free Software, but you can sell things that take advantage of Free Software as a resource.
I'm not even buying the premise. Any business can look at its bottomline to see if their advertising works. If they can't, then its not working.