The problem is that you never know, which type of activities may be considered as Suspicious by a particular casino. Big wins I think are always treated by any casino as the case for additional check.
What is considered to be big depends on the casino itself, if we are talking about a casino that has been around for a very long time then most likely you can win thousands of dollars and still not go through any kind of additional check.
Still as long as the casino has a good reputation and you are following their TOS then you have nothing to worry about, the problem is that many times people select the casino in which they want to gamble based on the bonuses they will get and not on their reputation, causing them to play in casinos with dubious reputations that will do everything they can to avoid paying their customers.
Just use your common sense then you would likely to save up yourself in lots of troubles specially on dealing with a shady casino or even just new ones but somehow we couldnt
really make out conclusions yet until its proven thats why there are people who do really love to dive in when they do really see some interesting offers and bonuses
from these new sites which it isnt bad but you should be wary on possible things to happen but if you do really make use your common sense and will on the right
way then you could totally make out some initial observation whether its a serious business or just simply a trash one which is just trying out to get some deposits.