Many eBay sellers don't ever purchase, store, stock, deliver any merchandise at all. Instead, they use a method of delivery known as dropshipping.
This is a method whereby the seller places an item for sale on eBay, at whatever price the seller chooses to charge for it. Once a buyer has paid for the item, the seller then pays the supplier who actually has the item in stock their price, and the supplier ships the item to the buyer. The seller can keep everything that the buyer has paid over the seller's cost of the item as profit.
This can be a very easy and effective method of running an eBay Business if you have a good, dependable drop-shipping dealer. If all things are running as they're supposed to, then the process should be a smooth one.
However, if you aren't diligent about doing your homework (again, check with the Better Business Bureau!) you could end up getting many, many complaints from your buyers.
I have seen all to often when an eBay seller who uses a dropshipper has successfully ended auctions with bids, the buyers have paid their money, the seller pays the drop-shipper only to be told then that the item was "out of stock" or shipping would be delayed.
Then, naturally the buyer starts emailing, calling on the phone even, wondering where their item is that they've paid for. It doesn't take long before they start filing complaints, initiating charge-backs with their credit card companies, and inundating the seller's eBay account with negative feedback.
Don't let this fact keep you from exploring the dropshipping possibility, though. Most sellers have no problems with this type of situation if they are dealing with reputable companies, so just do your research and know who you are dealing with.