Don't sell stamps, but have been buying a lot over the past two years. In the past 6 months I've transitioned from
ebay being my primary source to Hipstamp. Found that (I am generalizing, just to be clear) there tends be a lot less weenies there, and being stamps-only; it is a lot easier to find what I'm looking for as searches only really have to factor in stamps/philatelic material.
I'll sometimes use
ebay as a "check" as you never know when someone will list something for a lower price, but just from one buyer's perspective, I prefer Hipstamp. Only issue I have in general is you have to manually check the shipping rates as they don't appear on the item listing. Kind of a pain, but I do check, as I've made the mistake of buying a $2.00 stamp and then seeing $3.50 in shipping after the fact.