How to do service trades?

Hi, I read on forums and reddit that you can get flagged for making empty trades for services (trades where you get currency but you do not give anything).
I provided act carry service and made number of empty trades on my previous account and got banned for third-party (ofc I do not know the real reason since it is policy to not reveal and there are a number of reasons under third-party ban).
Is there any way I can avoid getting flagged for doing trades for service or should I avoid them on my new account?
Or is this all false and I am paranoid.

I am not asking about bans this is simply a query: Is it safe to make empty trades (trades where you do not provide anything in exchange stash tab but you get currency) for services?