One of the most reliable predictors of crap is a cover letter that tells me how well edited the book is or how many novels are under the bed.
Have you ever noticed the people who feel compelled to tell you how honest they are, aren't?
How handsome and how much the girls admire them, aren't?
How important and powerful they are, aren't?
People who are honest, courteous, smart and witty don't need to tell you. You know it by looking at them, listening to them, and reading their pages.
Show, don't tell, starts at "Dear Miss Snark" not "page one".
Don't tell me about the hours you sweated in the gym. Show me the beefcake.
LOVE that last line. I may have to frame it.