I've been in a critique group for three years. One member is a retired editor, which has certainly helped.
The group hadn't read my query before I sent it out though, and that was the problem. The query sounded as though I had grown up as Oliver Twist, and the ms sounded as though I was Mary Poppins.
Egads! I solved the problem, mailed more queries by email, and suddenly everyone I send it to replies in ten to fifteen minutes wanting a partial of fifty or so pages.
What shall I do if I get an offer for representation (wish!) but I really, really want to go with an agency that turned my partial down (before I corrected it)? Would it be rude, annoying, presumptuous, to go back to them in an email and say, "You rejected my partial, but now I have an offer for representation on my manuscript. I would much prefer to be represented by you. Would you reconsider?"?
You've got an offer from Miss Snark in your hot little paw, and you want to use it as leverage to get someone you want MORE?
No. You can't do that.
First, you don't know if Agent Snark and Agent Bark know each other. You want to find out the hard way that we're on the same roller derby team and talk to each other?
Second, you guys are getting all caught up in this lunacy of "dream agents". This is akin to breaking up with your boyfriend (who likes your mom, walks your pink tammed, cigar chomping poodle without complaint, and cooks!) because you want to marry George Clooney.
The only question you need to answer when you get an offer of representation is: is this agent a good match for my book and me.