Are you talking engine rebuilds, etc? I was in your shoes once. I have no formal training in engine troubleshooting or rebuilds, but I consider myself pretty good at it. About 12 years ago I bought a blown up quad for the first time as a money making and learning opportunity. It took me several months, but eventually I got it running and looking good again. It was a fun project, and I made some good money to boot. Since then I have been hooked, and do several flips a year, and also sell parts on eBay all the time.
Rob
Rob