I was writing this, so some of this was covered by marmalady just now.
A few more thoughts.
Can you do lookups in your home area for people whose family have moved away? For example, 'my gg grandmother was born in <your town>, can you find her birth record? It's not online."
Figure out what you can do that someone can't do for themselves in a few hours at the library.
Pick a price per hour for open ended research, like "my grandfather left his wife in the 1920's and was never heard from again. Can you find out what happened to him?" -- If I had $1/hour for the time I spent looking for my wife's grandfather I'd be a rich man. Many people might not be interested in their whole ancestry, but they have one or two questions like that, or a family story they want proven true or false, or a skeleton in the closet, etc. Lots of questions on rootschat also center around "out of wedlock" children and trying to find them. Can you do that? And finding birth parents for adoptees, and adoptees for birth parents.
And the hardest part of getting started is figuring out how you are going to get the word out widely enough to get customers. For my real job, I went from store to store and office to office with calling cards. But genealogy research is a bit more difficult. I never really got past that hurdle. If you do a few, you might start getting word of mouth references.
When I said above to just pick one family and do it, maybe do a friend's for free, preferably a friend with a lot of other friends they can tell
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Talk to your local library's research librarian. He/she might get requests for more than they will do in house, and also might know others doing the same work you are trying to get into. Also, is there a local genealogy society? The members would be your competitors to some extent, but also might help network starting out. Weigh the two and decide.