You simply key in a search term and the tool emails you every three days with a list meeting your criteria. A robot does the work for you. Use the tools of the Information Age to your benefit in expanding or contracting your time frame. Don't let an auction bid cycle work you into a frenzy and hurry your bidding process. Online auctions work for most items that can be shipped easily or can be described with words and photographs.
Items still sealed in their original packaging are great online items.
One that comes to mind is a collectible automobile. With the restrictions of an online auction, it may be hard to establish the condition of the vehicle. If you can have an independent third-party inspect the vehicle, than you may be all right. Maybe you could have an escrow company hold your payment until you are satisfied with the item as represented by the seller. This would be something to negotiate with the seller before bidding.