It's 11 o'clock on a quiet weekday morning in a scruffy Lancaster neighborhood, and the Pallet Kings already have sold 15 of the 32 pallets of merchandise that came into the store just an hour before.

If you’ve ever heard of return pallets for sale and have wondered how to buy them, you’re not alone. Many “overstock” or “liquidation” centers are popping up around the United States, but how do they ...