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, well or better still trade with signals while learning, this will actually boost his knowledge in trading.
Most signals are only good for the pocket of those giving signals. So like for example, I noticed that trading signal groups, you can't really get profits from their signals, more likely, you will be on the losing end. Why? Because the owner themselves are benefiting from it, not the subscribers. Usually, you are already too late to catch the right time to buy or sell. Be careful also joining this group because you may end up holding worthless coins.