I wwoofed for about 2 years. The farm I stayed at the longest gave wwoofers commission for working markets and festivals. It was inconsistent but still nice, and I did get occasional paid gigs from neighbors and my farm mentors (i didn't have a car). The farm work and cooking etc took up a lot of time however so I wouldn't have wanted to work more than 10-15 hours a week on top of that, because wwoofing can have a lot of perks in the off time. It is also great to sort of forget about money while wwoofing if you have the luxury.