A casino is a for-profit comoany and they have to make a pre-determined income in order to remain profitable and don't find themselves forced to shut down their doors. The percentage of profit a casino has to make does not differ much from one casino to another, it's almost the same.
So, if a casino is offering huge rewards and/or bonuses, be sure that they will componsate somehow (ie. higher wagering requirements, higher house edge..) and vice versa. It's up to the player which plan suits him more but the end result is always the same.