When buying a phone from eBay
, make sure you're first of all buying from a reputable seller with at least a 100+ items sold and a decent seller rating of at least 95% ... any less and I get a bit antsy. I personally try to buy expensive items or "risky" items from sellers with 1000+ items sold. A lot of those sellers are phone dealers and often include a website, location or phone number in the ad.
The next thing depends on the phone. If it takes a SIM card then make sure the phone is either unlocked or has the Sprint logo on it to ensure that it works. If it's an older phone that uses CDMA you can ask for the ESN # located under the battery and call Sprint to verify that it can be used on their network. The last thing you want is to buy a phone that can't be activated on their network without actually unlocking it yourself which can be a pain. :(
I've bought a couple phones from eBay and never had any trouble. A lot of people have concerns about shopping there but I've been active on the site for many years and never had any trouble.