Beginning your letter with something along the lines of "Your years of experience in YA book sales make me feel that you are the perfect agent for me" will probably get you a.) mocked, and then b.) rejected. And then, c.) mocked again for good measure.
Why? Well, because as most of you know, I'm a brand-new agent and as such I actually don't yet have any sales under my belt. Or under my bed. Or under the litterbox.
Just something to think about.