I started out with an eBay store, and expanded to Facebook Marketplace and Craigslist. I'd say about 50% of my sales are on eBay, 40% on FBM, and the remaining 10% through Craigslist - but it changes a lot based on time of year and what the product is. Windows XP machines almost exclusively sell through eBay; more expensive machines almost always sell through FBM.

Most of my buyers buy one machine and are done, but a substantial subset are return customers. Return business is all about the usual stuff: Reputation, level of service, quality of the product. I have a few "regulars" who have bought 4+ machines from me, usually hobbyists or small business owners with a specific need. Having done this for a couple of years, I also now get return customers semi-frequently who bought something a while ago, like it, remember me, and seek me out again.

I don't offer warranties or guarantees on items, but I'm aggressively inexpensive compared to the competition, and I operate on an informal "if I broke it, I fix it" policy. If I told you something was working and then later it breaks, I either fix it, swap it out, or replace the machine.

I have a five-star reputation on Facebook Marketplace and 99.6% positive feedback on eBay as a result of this policy, so it works decently well.