Affiliate codes are 15% off your order. Promotional codes from Edens, used for promotions and special sales vary, check the static on the front page or the promotions at the top of the page. You also have the option of a buy out assignment which is put in yout assignment cart by using the 'grab it' option on the top right of an item page. This is 30%, received when you actually go to your assignments page and request it. You are limited to six at a time and must complete the reviews before ordering more.
also, you get the 3% commission if someone (self included) uses your affiliate link. If you get a banner with your affiliate code in it, you'll get 20% commission, though they clicker doesn't get any discount. It's helpful when placing your own orders though. Imo.