No one can be sure of anything, otherwise, everyone would've become rich.
The signals that are offered by some services and telegram bots usually predict the price increases based on the sudden increases in trading volume.
I like the part you said if the market could be predictwd then everyone did be rich, well it's true tho. For me I would advice a person new to crypto shouldn't just trade with signals alone, they should try to learn and make thier own trade which will be best for them, because a good singnal wrongly used could still turn out bringing a bad trade, so it would be better to learn first before entering the market.