I'd expect for $175 that it would be a good machine. That means plenty of meat on the reel for multiple future resharpenings, good chains and sprockets, a good catcher, a Briggs engine, and essentially, nothing much to spend to get it into prime mowing condition. In other words, that sounds like the price for a good one. I'd expect a non-running one of uncertain provenance, with no catcher, but with a good reel (i.e. lots of resharpening potential) to be in the $50-70 range. I suppose I'm a relatively keen shopper, but with what it will cost to replace all the chains and sprockets (which are usually shot on randomly selected old Scott Bonnars), sort out the clutch, buy a catcher, and do something about the paint and decals, it would easily owe you $200 by the time it was ready to use. You should be able to buy one for that price that is already good and needs no more than sharpening, adjustment and a tuneup. Why do all the work for nothing, and risk getting nasty surprises along the way?
I seem to have seen reports from Outdoorking members of buying very nice SBs that haven't been used much, for around $170. These are machines that may have ratty paint and need a sharpen, but are otherwise good to go for a decade or two. Just be sure and check the condition of the chains and sprockets, that it has a good catcher included, and that it hasn't been used to mow water pipes or old bolts, so the reel is undamaged.
