It's tough. Linuxcare, where I worked in the dot.com days, wanted to be the support company for open source software, but they got derailed by ... other issues.
Most of the 'successful' open source companies are not just straight up service outfits. Redhat, for instance, has a model where you must buy a subscription, or you don't get support. In fact, you can't even use Redhat if you don't buy a subscription. They do this with some trademark trickery, which creates some of the artificial scarcity that open source software lacks.
People's time, is of course scarce, but services can be difficult to scale, as doing so requires people/management skills much more than actual technical expertise, or some kind of product. Also: to be profitable, a services company should spend as much time as possible billing for services, which may come into conflict with time spent on things like building a product that is then given away.
Most of the 'successful' open source companies are not just straight up service outfits. Redhat, for instance, has a model where you must buy a subscription, or you don't get support. In fact, you can't even use Redhat if you don't buy a subscription. They do this with some trademark trickery, which creates some of the artificial scarcity that open source software lacks.
Somewhere, somehow, something has to be 'scarce' to be able to sell it: http://journal.dedasys.com/2007/02/03/in-thrall-to-scarcity
People's time, is of course scarce, but services can be difficult to scale, as doing so requires people/management skills much more than actual technical expertise, or some kind of product. Also: to be profitable, a services company should spend as much time as possible billing for services, which may come into conflict with time spent on things like building a product that is then given away.