I've said it before, and I'll say it again: writing and sending your own query is an invaluable part of the publishing process. You have to do it. Paying someone to do it for you is akin to paying someone to learn hopscotch for you: they can hit every square from twosies on up, but you'll still be standing there holding the chalk at the starting point.
If you want the latest evidence of query writing service failure, read Rachelle Gardners very nice, very temperate, very polite blog post. Me, I just let Priscilla deal with 'em.