I'd say buy 1 or 2 machines and sample it first. It's a lot of headache to deal with ebay, ~15% fees, income taxes if you do it legally, shipping costs + travel costs to ship, boxes, packing, etc. Some
parts sell super well, others there's 30 listed and the lowest price is like $10 with free shipping and the seller is likely loosing money when it sells. Also depends on the model, some sell well, others aren't so well. Anything 250r, 350x, 250es, 250sx normally does pertty well, but if you got one of those machine cheap, I'd say to try to fix it up, or get two and make 1 out of the two.
Anyway, good luck if you go for the buy and flip the
parts route.