What you shouldn't do is, when a casino delays withdrawals or feels slow, accuse them of various things, like fraud, for example. That's overkill. However, if it's just criticism and suggestions, I think they're perfectly valid. After all, customers have the right to make suggestions.
Users can complain, make suggestion or anything else but they should do this politely. It is more acceptable and comfortable to receive complaints or suggestions in polite ways in business side and with users, in user side by making their voices in polite ways, they increase chances of being listened and reduce risk of bad treatments from companies.
Companies, if are legit, won't treat their users badly even users have bad mouths or contribute suggestion in impolite ways. However, as users we need to protect ourselves first and being polite is one of ways of self protection.
That's how it should be. Even though they require the best possible service, we, the ones who will submit complaints, criticism, and suggestions, must also do so in a respectful manner. I'm sure they won't turn a deaf ear because they don't want to be abandoned by their users.
Conversely, if we convey it in a negative manner, they will feel uncomfortable. I personally prefer to look at myself when doing something. When others approach us, we naturally determine which method makes us comfortable. And if we feel uncomfortable, then the same thing we do will make others uncomfortable too.