We have purchased refurbished laptops on ebay with no problems. Generally the refurbished ones come with some kind of warranty. Just check for the sellers rating - the closer to 100, the better.
This summer, we decided that we wanted less expensive computers to take on vacations so that if something does happen to one, it is not our main computer with everything on it. That is where the refurb ones come in. I am using one right now that I bought on ebay in August. I wanted a netbook and got a good deal on one. This has been the first vacation that I have taken mine on and have had no problems whatsoever. It sure beats lugging my 17" laptop around.
My husband bought a used Dell that is almost indestructible model to use outside with no glare while on the beach, deck, or around the pool.
He also bought a refurbished 17" Toshiba last year so he could have one like mine. It works great and cost $200 less than the one we bought new.