Many of the telegram groups which give signals are run by the same people, I have noticed on multiple occasions of the groups giving the same signals. Many of the groups also conduct coordinated pump and dumps, and they usually send it in all the groups to gather a greater audience. Although some of the signals turn out to be correct, always do your own research before making a trade.
I agree with you. Some telegram groups are not reliable and it is not actually accurate and in the latest happening in an ico. However, if the telegram is really accurately connected to the project, it is just fine to trust it. It is still best to gain news in their forum and whitepaper.