The requirements for withdrawal shouldn't be exceptionally high or else it'll be nearly impossible to legitimately withdraw anything you might earn with bonuses, but at the same time making them low does mean people can abuse the system as others have said here. There's really no easy solution to this problem, and as a result I really don't take advantage of deposit bonuses very often as I find it is usually very hard to withdraw any funds you get with the bonuses. If you're ever unsure of what the minimum requirements for withdrawal are, reading the terms of service or terms for the promotion should show you that.