I got this in PM, so I'm going to answer so no one else has to ask.
how does it work?
Ebay gives you $1 in ebay bucks for every $100 you spend, but you'll only get to use the certificate next quarter. Quadruple ebay bucks promotion means you get $4 for every $100 spent (basically 4%).
So whatever you want from ebay, I'm willing to buy and have it shipped directly to your address, then we split the promotional offer (2% for each of us).