I've purchased a vaporizer and vape replacement items with no problem off ebay. Many of the vendors are vape companies. I think it's vapenow that sells there as warehousegoodsonline. I've had no problems whatsoever. There was one vape that I bought that came with the whip broken. Turned out that it was new, but from a pawn shop. We negotiated how much it would cost to replace the piece and he credited my paypal account. So even then, no problem. Also, if I'm not mistaken, ebay will protect your purchase, especially through paypal. So, if you are sure you are buying a reputable product, there should be no problem.
Edit: the other thing you want to make sure of is that the vendor has 100% feedback rate