Think a bit about it.
If their signals were so good, why would they sell them to make money?
Why spend time and money to create a structure to sell something when you could be using the same time and money to use those signals to get a lot of money?
The only signals i would trust would be ones from people that i know, that i talked about what is his strategy, and after he showed me some trading history.
Trading is a mix of feeling and knowledge.
Feeling to understand when the knowledge you have can be applied.
Here is a great book to start on the path of knowledge: https://www.amazon.com/How-Made-000-Stock-Market/dp/1614271690
It won't teach an amazing technique to be a millionaire, but it is a first step to understand what not to do.