I've been doing this for about 8 or 9 years now. When I started, I thought I would hunt games, fix them and then sell them. What I actually did was find them fix them and pretty much keep them. The hunt was my favorite part. I would only sell games if by chance I had a duplicate or was simply out of room. But...the "hunt" was the best. Wasn't so much about the money, but finding gems. When I started, there were probably 20 people in my area hunting games. I can't imagine how many there are now. I used to regularly travel 3 states in my quest to find good deals. Totally agree with Arcadius.. Don't just buy any machine trying to make a profit or you will get stuck.
Frankly, the popularity and awareness of pinball value has grown so much, the hunt is pretty much dead. Too many people after too few games. I had not bought a pin in over two years when just by chance I checked CL and there was a fresh South Park for $500! Said it didn't work but really all it was an error. Ended up being just some minor corrosion and a bad ram chip (obsolete chip, but Digikey did have another compatible) I was first call and the machine was within 3 miles of my house...By the time I got there, the seller of course had higher offers. I asked what they were and he said $650... So I paid $650 for it.
Unless you have some inside line on machines for cheap, I can't imagine anyone thinking they can hunt fix and sell for profits these days....unless you value your time at $0 per hour.
So...find machines you like at reasonable prices and simply enjoy the hobby. Maybe you can fix it up some and get a little more for it when you sell it or maybe trade it..
I lost the hunt so now I do other fun things, like make new clear and colored ramps for games that no one else cares to support.