I received an email from trading brokers that I can lunge my funds with them and they execute trades on my behalf but I am afraid of the legitimacy of such services because most of them always turn out to be scammers.
You have missed to include more information about the broker who sent that offer. Because, only based on their credibility level, you might need to decide whether to invest with them or not. Because in some countries, there are registered brokers who are offering such services in profitable way but they might be taking some big portion of profit as a cut for their services.
I believe no one will be having any problem to pay some fees to a trading company after getting profit. It might be hurting only when we need to pay fees after they produce losses. Yeah, some brokers will collect such fees well in advance hence you need to pay those fees whether they are getting you profits or not. In my country, we are having such services in the name of mutual funds and non-registered brokers also doing such profit sharing way of trading in unofficial way.
I have not tried anything like that till now because I have been into bitcoin holding which is more than enough for me to make my savings work for me to get good returns over the time.