I would check the used one out very closely in regard to condition. If it has been stored outside for over 4 years that would be a factor for me and I would question the "only used once" explanation. When I was looking used, I found that these units do not stay around long as people scoop them up quick. That is the main reason I bought new, plus I got a great deal. I did a quick search on CL for you and found nothing locally that you could consider. If it were me, unless they came down to at least 2k on the price, I would be considering new. As was already mentioned, you might want to at least check out the Pronovost and Farm King line. These were the two that I narrowed my search down to before I bought mine. That is not to say that the other brands are not decent units, I was just very impressed with the reputation and construction of the Pronovost units.