I have found that BT headsets always fit differently on every person. One that fits me, might not fit a client of mine. Although I could sell them the H500 or H850 because it fit me right, it doesnt mean that they are going to enjoy it.
Rather than spending the money on Ebay, swing down to your local store and check their prices (you might find they are pretty competitive...especially with Rebates). From the store, you can find one that fits, thats new, and that (most likely) has a warranty for at least a year.