i don't know much about merchant sites other than amazon and have been browsing newegg for the first time today and discovered "mail-in rebates", what are those?
Mail-in-Rebates are essentially a process in which you can recoup some amount of the purchase price back. Essentially it works as follows.
Step 1: Purchase the product with a mail-in-rebate special for the full price displayed
Step 2: after purchase you'll receive either a coupon, receipt or a form to fill out and mail back to the place of purchase.
Step 3: Wait for the rebate as it can take quite awhile. Rebates can come in many forms from a cheque, in-store credit (essentially a balance added to the account associated with purchasing on the retailers website).
For Newegg specifically see here
You need to pay full price and wait for the rebate.
You send in your receipt/product label, you get mailed back money.