Having looked at some signal providers there seems to be be some unhappy customers who have not had things explained well. Stop losses and take profit has to be a pre-requisite so at a glance anyone who subscribes will know the potential risk prior to taking any action to subscribe, also lot size must be explained and understood that large lots will increase an account but will also decrease an account, it is much better to start with the smallest lot size and increase when the fund is growing.
Losses can occur, on inspection a subscriber should be able to see some kind of ratio between past trades that made a loss and profit, however the past trades cannot guarantee what future trades will be, but one can only have faith in the signal they are subscribed too. Many losses do not make a signal service bad, it can show responsibility from the provider, it can show where the provider wants to start a process again, possibly the setup has failed and a failure level has to be set to stem larger losses, which I am sure you will appreciate
A possible trap that a subscriber can fall into is the subscription fee and how paying a monthly must have to be made up with profits, not the case.
when joining a signal service you will never know if you are on a winning curve or a loosing one, small steps and caution should be taken in the first instance, confidence in the first profits can be met with raising the lot size to a possible level where no one loss can erase them, this way a break even or possible missed subscription fee can be made but at least your still in the game.
MQL should have two pricing structures, an introductory and full price, this would encourage subscribers and give them a chance to trade small in order to possibly make the full subscription fee, also give confidence in their choice of signal providers.
These are just my thoughts and no advice is intended, choose well.