N, R at 8th St.-NYU; 6 at Astor Pl. Hang out for a while at Flight Club's nondescript Greene Street location and it's easy to understand why this concept store is giving eBay a run for its money.

4, 5, 6, L, N, Q, R at 14th St.-Union Sq. Stocked floor-to-ceiling ... The process is simple: Flight Club lets the seller set the price, and the store takes a cut of the final sale.