After reviewing the site mentioned, [Bidz.com] it is clear that it gives a grace period of five days to pay the price after the purchaser wins the auction, and nothing will be shipped until after the price has been received in full. It says on the site: “Payment Due Within 5 Days. Payment on any Product is due promptly, but no later than two (2) days after Bidz.com accepts your offer to buy a Product. Any payment not received within 5 days of when Bidz.com accepts your offer to buy a Product will be referred for collection.
… Time to Ship.Bidz.com will not ship Products or begin to provide services until full payment for such Products or services is received. Bidz.com will deliver Products to the shipper within five (5)business days of receiving payment for such Products. During peak season, your order may take longer to ship. Additional services such as ring resizing or gem and jewelry reports may delay your order up to seven (7) additional days.”
Based on that:
It is not permissible to buy gold or silver through this website, because it is stipulated that there be an immediate hand to hand exchange when selling gold and silver for gold and silver or currencies. This hand-to-hand exchange does not happen in this case; rather the product is not delivered to the shipping company until a few days after receiving the price.
It is permissible to buy items other than gold or silver by the method mentioned on the website, because there is no stipulation in sharee‘ah that there be a hand-to-hand exchange between the two parties (the seller and buyer) if it is not a sale of gold or silver for cash