I suggest that you buy on eBay and filter by "New", which is what I did with mine. I verified that it was unused by going to Apple > About This Mac > System Rep

I suggest that you buy on eBay and filter by "New", which is what I did with mine. I verified that it was unused by going to Apple > About This Mac > System Report. Then select "Power" and look for the "Cycle Count" under "Battery information". This will tell you how many times the battery has been recharged. It should be a very low number. I think mine was 0 or 1 when I bought it. eBay is also pretty good about returns if anything is wrong with the laptop. Good luck!