Rakeback 101. Rake is whay you pay to the site for hosting the game. It comes out of the pot before it is awarded to the winner of the hand. Each player at the table is responsible for some of it, even if he didn't actually bet in the hand because he's sitting at the table actively involved and pays his blinds when it's his turn.
Let's say that you play for 4 hours at one table and see 200 hands. Each hand is raked some amount (anywhere from $0.00 when everybody folds and the big blind wins by default to maybe $3.00 in a huge pot at high stakes), and after the 200 hands there has been a total of $120.00 raked by the poker site. Each player is responsible for generating a percentage of that $120 and you figure it this way: Imagine that over the course of the 200 hands there has been an average of 9 players active for every hand. $120 divided by 9 = $13.33 so each player has generated $13.33 in rake for the site.
Although nobody actually monitors you play in terms of how you play, the poker site will report the amount of rake that your account has generated to your affiliate because they pay him a percentage of that amount as a referral fee. Forever. For as long as you play on the site. No wonder everybody wants to be your affiliate, eh?
If you have signed up for that poker site through an affiliate who offers rakeback you'll receive a percentage of that $13.33 as a rakeback payment for that session. If you have a 25% rakeback deal you'll get back $3.33 for this session. The affiliate can afford to pay you because he gets more than 25% from the poker site as a referral fee for finding you and signing you up as a customer of the poker site. He may get 30%, pay you 25%, and keep 5% as his profit. It's free money for you so you should always try to secure a rakeback deal from a trustworthy affiliate.
"is it safe? legal? do the sites know about it? if so why dont they just offer it. can i get rake from the past?"
It's safe as long as you do business with a reputable affiliate. Do plenty of homework and normally ignore those who solicit you. The good ones don't need to. There is absolutely nothing you can do if your affiliate decides to just keep the money.
It's just as legal as any other online-gambling-related activity.
The sites know. Some approve; some disapprove but look the other way; some will freeze the affiliate accounts if they find rakeback being offered. In any case, the player is safe. The poker site wants you. They do offer rakeback...they offer yours to their affiliates.
You won't be able to recover any of the rake you paid in the past.
Happy hunting!:digit: