Alternative online auction sites may not provide the same level of buyer protection as eBay, so you may want to consider using an escrow service to protect yourself. This protection comes at a nominal cost, and any reasonable seller should be willing participate —if they are legitimate.
I use an escrow service, when the item is more than a few dollars, and I have little knowledge or experience with the site or seller. The fees can vary a lot, and as the buyer, you will be responsible for all extra costs incurred. If you are wanting next day certified check service on your monies you can expect the fees to start at $35.00, they will be less if you are being mailed a check or money order at the discretion of the escrow service. You pretty much get what you pay for.
Using one of these services will protect you from not getting an item, or getting something other than what you have paid for. The decision is all about how much risk that you are willing to assume.