this is essentially what plenty of people do on this forum, and more specifically in the Official Thrift Brag Section. I do this very casually aka spending 2 hours in thrift stores a couple of times a week. Granted that thread promotes a really neat culture of trading and not-for-huge-profit bartering, it is still a really great resource. My area isn't the most consistent to thrift in, but, with a discerning eye, I have managed pick up several items and quickly sell them up to 21x my cash outlay on eBay. I am doing this purely as a hobby and therefore will probably never make a living or a viable salary off of it. But, it can buy me and the misses the equivalent of an iPad and a nice boozy dinner each month then I am happy. I can see the possibility of this being a viable business - there is a 'Men's High-End Second Hand' consignment shop in my town and it seems to stay afloat in a decently high-rent building.
What about a model where your store has a small B&M presence and also delivers another service that pulls members of the 'cute downtown' into the store..or partners with another venture ... say upscale men's hair boutique that has scantily-clad hairdressers.. say an ice cream shop or something that can cover some of the monthly expenses more readily than the consignment / 2nd hand clothes.
I think your audience and customers are far more likely to buy from their couch on a sunday evening on eBay.
yeah - as said, I would buying items at your basic thrift prices. In some cases they are fixed to the type of item, in other cases they vary with the brand. some do discount days as well. That said, I think you can take an item out of thrift store, and mark it up at a higher price point. My supposition is that people would be more willing to spend money on a cultivated collection of higher end merch at a 'resale' shop vs going to a thrift store. Not outrageous, but if I could buy say a polo button down for 3-4 bucks and mark it up and sell it for 15 - 20 bucks, I think there may be something there. same with jeans, tops, etc... and thats without touching women's stuff, I haven't fully thought that through yet.