Make sure that the condenser lenses aren't scratched. Also, check the nylon gears that move the assembly up and down the track. If these are hosed, you'll have issues.
Great enlarger. I love mine. Also paid $100, but I got 2 cones, 2 135mm lenses, a 50mm lense, trays, safelight, bulk film loader, 2 film coloring kits, 4 stainless 35mm reels, a stainless tank, some patterson tanks, and a few other tidbits. I think you can see where I'm going here. I'd offer them $75 without a lense and board I guess. But it is still a good deal at $100.
Use the flat board and the top lense at the lowest position for both 50mm and 75mm. So you'll need 2 flat boards if you do medium format.