They don't want the appearance of tampering. They don't really care about tampering itself because they make their money either way.

So as long as you are subtle about it they won't even investigate, as a public investigation would make it seem like tampering was common.

I'll tell you another thing that will risk their cash cow - a reputation for not paying out when gamblers win big, because of vague and specious accusations of fraud (which the gambler denies)