It is dependant on which area of business you're wishing to become trusted within, I would first start of with making a vouch thread, here -
http://www.sythe.org/vouches-forum/ ... Then depending on which field you're interested in, make a shop, or thread offering your services. Whether it be within Account training, buying/selling, Gold Swapping buying/selling, Names, GFX, etc.
Then build up a reputation, vouches, whether it be you going first, or them first, etc, simply build it up and in the end if people wish to purchase your services, your trust aspect will depend on that.