RSVP's allow buyers who can't find what they're looking for to post a free "want to buy" ad. Sellers can respond to the RSVP by posting any of their current listings as an item of interest or an "offer". If a seller has no active items, they can list a new item in response to the RSVP and submit it to the buyer for consideration. The buyer can then select an item of interest and make a purchase using the buy out methods offered by the seller.