Many signal/system sellers face this question: If your signals/system are really as good as you claim, why do not you trade them yourself? Many sellers could not answer such question, or stay still not knowing what to say!
I am not going to defend system/signals sellers, because many if not most are scammers. However, there are real honest ones. Some of those real honest ones fail at some time. Some continue to win.
Now stop for a while. Think for a few seconds. Assume for some moments that you, as a trader, discovered a system which works very well; A system which is a winner; A system which accepts losses, but overall is a winner. A profitable system which makes 200 pips a month on average.
Now ask yourself a question. What is better, to trade this system yourself and never tell anyone about it? Or sell this system/signals for other desperate traders?
A good marketer can find 200 subscribers for his system at a rate of 100 USD per month. This will bring an income of 20,000USD per month for this seller. Let us be more pessimistic, suppose he could only bring 50 subscribers. Then his income would be 5,000 USD per month.
This income comes stress-free. He is sure about his systems, but there are some losing months, however his system makes 200 pips per month on average. (An average promising system.), but why put himself in stress. Maybe he is not disciplined enough to follow his own signals? Maybe his system needs a 25,000 USD account to pass the biggest drawdown, and he is not willing to put such an amount in trade.
So, my opinion on this matter is do not attack system/signals seller just for the sake of attacking. Do your own diligence. Beware, maybe 90% of signal sellers are either scammers or do not know what they are doing. But there are a few signal sellers out there who are honest and provide a good reliable service. As you read those lines, you yourself could have a good system, or you yourself could be a good trader, and all of you know that there are 5% of traders who are winners. So why should not one of those people have a signal provider service? There exist such people who provide it.
Finally, the only thing that could protect you from scams is doing your own diligence, read ratings at other sites, read the signals seller own forum, pose questions, and conclude the result.