So...is this the logic of parts*3 that mechanics use?
Let me explain. The process as I understand it is:
1) Receipt into system and packaging
2) Review and reconditioning
3) Storage until shelf space becomes available
4) Stocking
5) Sales
6) Shrinkage
1, 4, and 5 are done by low paid and low skilled laborers. 3 is what we like to call overhead. 2 is where the bulk of your variable cost lies, and where a card can either be dusted and checked or just dusted depending upon final sales price. If shrinkage is somewhere near 20%, which is bit on the high side, and sales is 20% of the final cost, 100-20-20-50 is what you can spend between reconditioning and storage, or about 10% of the price. That seems about right given how little is assumed of labor, and it explains why they "trust" a bunch of teenagers at the geek squad to pull this crap off...because it's the only way to profitability.
That said...because it is feasible to have $160 for a thing you resell at $320 doesn't mean that it's a good deal for either you or the purchaser. If we cut the difference, and require a specific demonstrated benchmark, then you could buy second hand for $240 and both the seller and purchaser come out better than buying through a middleman. I...am looking at a 580 right now, and I watch these things go on newegg for about $100...but they are selling on ebay for $70ish. Unless the retailer's warranty is something you trust...it makes little sense to buy a used card from any of them.
As a hint on my personal stance, I view it like travel insurance. On a $500 trip it costs $70. It only activates if you cannot go due to some recordable illness of insane event...so it doesn't insure you against things like airline maintenance incompetency, weather, or even a death in the family precipitating changes (unless that dead person is one of the passengers. That's the kind of insurance most large names stand for, so why pay extra for literally nothing?