Upwork: This website offers a great marketplace for selling just about any professional service. You don't need a merchant account, website of your own or anything else for that matter. All you need to do is be able to provide a high-quality service at a reasonable price. But be informed, you will have to compete with many others that are constantly bidding on open jobs.
My next self-funded business hit $160,000 in revenue in its first year alone. After that first taste of self-made success, I’ve gone on to sign consulting contracts worth tens of thousands of dollars with startups like LinkedIn and Google, launch profitable online courses, and grow my blog to over 400,000 monthly readers and $50,000/mo in side income.