I do not believe that. It depends on the type of gambling, for example in bookmaker betting through good analysis and a cool mind, but it is never 100% to win as some pseudo experts advertise. There is nothing certain in gambling. Absolutely nothing.
They can somehow be a guidance to a gambler but you're totally right that they're not certain and you have nothing to expect that much from them. But sure, if you're a fan of it and you're always looking forward to check them out, just hear them out but still decide whether you'd be following them or not.
Unfortunately, some people take advantage of people's ignorance or naivety to make money from it. This is very bad behavior.
That's the reality, if there are people that are ignorant of people's words and are gullible enough. They'd be seen as someone to be taken advantage of and they'll never start until they're able to make that much money from them. Whether we like it or not, there are those two types of person. The gullible and the deceitful.