I have had mixed results on E-bay.. Previously, I purchased a couple of Sprint version of the Sanyo Katana SCP-6600 phones successfully. I am still using one of them after more than a year. I have also purchased extended life batteries for them with mixed results.
This past spring, I was not as successful. I purchased two phones that I had to return. A couple of others started out okay but did not hold up for long. I purchased a couple of portable Wi-Fi units. One had the wrong interface and the unit seller refused to make it right. He did work with me to make it functional, but the MVNO (Mobile Virtual Network Operator) service refused to activate it. When they did, they screwed up the account.
I purchased a different portable WiFi unit before I found out the BYOD behavior of the third party service and that deal worked out ok.
I purchased a third Wi-Fi unit that was very functional. Sprint would gladly accept it, but I ruled the price of the plan to be excessive for my needs and sold it for a profit on E-bay.
At this point, I an trying to figure out what I want for my next phone. Sprint's current offerings fall short in one way or another.