I must be a n00b here, but I've really never seen anyone advertise a bodyguard service May I suggest 3 things? Throw up a couple of signs near the main spawns in the wild(s) for advertising - a lot of new players don't check the forums! Also, offer a rupee amount as payment "per x," where x is a legitimate time period. I'd say per 15 minutes. And, to protect yourself (and save us from having to settle a dispute ), take 1/2 of the payment up front and half of the payment after your services are rendered!
Actually when I first joined the server way back when, about a month after I had joined I started offering this service. I was one of the first to do so. I even had the sign up on my new shop for a while. Unfortunately most players were incredibly... um novice. So they read it assuming I would pay them to be my body guard. :S Also I only took on offers when I had time and/or ones that interested me. I charged as amount of time on the clock though. I did do it a few times for a few players who were interested and wanted to see what it was like. I offered more services though then what I listed, a player had to purchase my services to get the added bonus.