Many gambling sites have deposit bonuses.
However, if you receive the deposit bonus, there is a condition for withdrawal.
For example, 10 times the deposit amount, etc.
What is the reasonable condition you think?
Watchout! these offers comes from most of the scam sites so don't get scammed for some bucks.
At least check the receives about the site before depositing and if it is legit then you can try but this is just a strategy to make you play on gambling sites.
There are many cheats among betting companies, but there are also deposit events at major sites.