Am I allowed to ask a buy-in fee?

I just started my 07 skilling service and i'd like to know if this is allowed.
I basically want to hire workers for my service, but i'd like to ask a buy in fee, so that IF one of my workers scam, i can instantly pay back the victim. people are doing this on powerbot and it sounds like the safest option.

also, if i hire a worker, am i allowed to pay them 90% of the payment, and I take 10%, as a fee?
how do other people with a service do this?
thanks!

 

You have to set it up in a contract. Other users who have done this have had bad results.