You are right. If casinos want a friendly approach to gamblers they need to adopt a mechanism like you said as a warning to keep the rules clear and avoid any tricks that could be used by the house to avoid paying the gamblers later.
What kind of mechanism can you suggest? Such a pop-warning while players are currently playing gambling? It doesn't work that way. Gamblers should be responsible enough to read terms.
Whenever we are claiming a bonus or participating in a certain promotion, there's always a notice about it to read the terms. We should just accept the fact that we are lazy reading those terms so it's not the gambling site's fault if ever we are unaware or surprised that we already violate a certain terms.