I too have fallen (luckily) into repairing mowers as a hobby. I grew up helping my dad work on stuff at home and have always had a knack for fixing things and figuring things out pretty quickly.
It started for me about a year ago when I bought a go kart frame and built it as a Christmas present to my kids. I then proceeded to buy several go kart frames; I built a few but they turned out to be tons of work and not profitable.
Earlier this year, I bought a Snapper rear engine rider locally off of Craigslist for personal use. As soon as I unloaded it and put it into reverse, it had problems with the drive disc hitting the chain case. So, I studied it for a bit, and then proceeded to pull the engine making a quick and easy adjustment.
Let the snowball begin.
Since then, I'm scouring Craigslist every day, posting ads and use an Android app on my phone to advise of newly posted ads. I haven't kept a count of how many mowers I've flipped but I'm having a blast and making extra dough at the same time. I've even created a Facebook blog which is in my signature below.
Great topic!