$500 for a USED model? If it has been rebuilt then it has had a long hard life already. Heck both Sears and Menards here are selling brand new dual stage 5 hp blowers for just over $500 these days, unless the Honda is a big machine (26 inch and up, 8 hp and up) I'd be wary of the deal because the engine rebuild does not address transmission and other related issues. I would buy new for that much money.
Go to eBay - New & used electronics, cars, apparel, collectibles, sporting goods & more at low prices and do a search and find out what the model is selling for there.
I have a 10 year old hs724 honda on tracks. I paid 1,700 for it new and have never had any major repairs. the hydrostatic transmishions are very durable.