I have had great luck with the sellers I've used on Ebay. Do select the seller in the top ratings, not just the cheapest. I do have some advice though.
Be careful to research the phone you want to purchase. I didn't buy from Ebay, but I bought two identical phones from Amazon. I bought the first Samsung phone for myself. It was new and I loved it. I thought Mr. B would like it because it had voice-recognition software, and he can't spell. By the time I bought his, only used and refurbished ones were available, which should have told me something. I paid $50 more for his used than I did for mine new. After one month, his wouldn't hold a charge, so he had to order a new battery. I think it was $40, but it may have been more. Then we discovered that since it was powered by Zune, there would be trouble with updates to the software. I haven't had time to check into this, but Mr. B says that the phones can't be updated. I think he is going to the wrong website, but I guess I will find out.
The only real problem we have had so far is that we can't text photos, so we have to send them by email. I can't text out of some places and call out of others due to being able to hit a tower. I would say that's the carrier, but his used phone doesn't seem to have some of the problems that my "new" one does. I've checked the settings and they are the same as his.
Anyway, as I say, research the phone because even with a reliable seller, you may be buying something too obsolete to be of value.