I'm not sure about anyone else, but I've never bought mods out of the Mod Store. They seem WAY overpriced. Like college degree from Sanford Brown overpriced. (Google it if you don't get that). I have ...
It's hard to sell mods by mistake. You actually have to go out of your way to make that mistake so I disagree on the need for a buy back feature.
As far as the guy that said he's happy to buy a single mod for 3k crystals, you're off your rocker. Mods available for 3m is ok with me but I would like to see the crystal costs drastically reduced.