How much profit can I make? For each matched bet, you can typically expect to extract 50-80% of the free bet amount as profit. This is because betting exchanges usually charge a commission on winnings. You may also make a small loss on the qualifying bet due to the minor difference in odds on each website.
So when you see a book offer a Risk-Free Bet Up toR$1,000 it simply means that if you lose you'll get the amount of your initial wager back in something other than cash, and if you win, the book has decided that you don't really deserve anything extra.