Have you ever noticed how upscale hair salons are typically structured? A stylist begins as an apprentice, earning a small salary and tips. With time, he will develop enough skill to begin working on the floor as a stylist at the lowest pay scale the salon offers. Eventually the clientele will grow to the point where the new stylist will be very busy at that pay rate. The next step is to raise his rates. Most of the clients will stay with him, but a few will switch to the lower fee. This is quite ok because now the stylist will have room to gain new clients at the higher price. This process will continue until he reaches a level where he is not gaining any more new clients. If the stylist has the right personality and skill, he can go far. Of course, a stylist is only as good as his last haircut, and regular training is essential in order to improve in skill.
So what does that have to do with the interpreting and translating business? In the beginning one might opt to perform low wage work through agencies. It is a way to make some money and get busy. At some point though, it might be wise to raise your rates a little. The loss of a client or two will allow room to develop better paying clients. This process should continue until you see that you have reached your peak.
Constant study and training to improve your skill are necessary. People will only pay top dollar for top dollar work.