From their website:
The PISTOLPAY difference: We protect the Buyer by safely and securely taking payment from a buyer’s checking account or credit card, so that Buyers don’t have to release personal information to a Seller. We protect Sellers by verifying the receipt of the funds before notifying the Seller that the transaction has been funded. That way, Sellers can rest assured that when they ship an item, the funds have actually been transferred from the Buyer and are ready to be deposited. Finally, we hold the transaction funds until the Buyer has a chance to inspect and verify the purchase has arrived in the as-described condition, quality, and quantity.
Seems like it would be an alternative for many reasons; not least of which is PayPal will not deal with transferring funds for firearms. Kinda stupid for a business to turn down business but it's their call.
Amazon.com has a PayPal-like system for transferring funds but PistolPay is the only one I know of that will hold the funds until the buyer gets the product and has a chance to inspect it. This is especially good for firearm purchases. Both the buyer and seller get charged a fee which is dependent on how it is received. Credit card fees are higher than say a direct transfer from a checking account. Understandable.
Anyway, if you have ever wondered how to buy something or sell something and wanted to cover your ass, this is one way to do it. It's free to register.