Question: Ignore the idiots who want to help you (except me of course)

 Dear Shark Breath:

I sold my book to a small press. I'm going to receive a percentage on net sales for print, and a higher percentage for eBooks. They're good percentages. I'm happy. Who needs an agent?

Then I went to a writing retreat and an author I respect spoke about the importance of a good agent. (A)  He says my percentage will end up being more like 6 - 8.5%. (B) Then he asks, "What is your book going to sell for?"

I told him.

"So you'll make about a buck a book."

Pardon?

"What kind of advance did you get?

"Um...well...none, but what does it matter? An advance is simply a loan, isn't it?(C)

The author looked very sad and shook his head. "An advance means the publisher will work harder to get your book out into the world so he can make his money back. Get yourself an agent."

Rats.

Questions (finally)((and I sincerely hope they're not too silly, or insulting {too late, I would guess, after addressing you as Shark Breath}, or both)):

1. This author has won Lefty's, a Nero, and a Shamus. Does the publisher submit their authors for these awards, or does their agent?

2. Can I not simply learn from this, and for my next book negotiate a better deal, instead of sharing my meager buck a book with an agent? (Are you cringing yet, because I certainly am). I guess what I'm trying to say, and not doing it very well, is will an agent really get me that much of a better deal to make up for paying him/her? Wouldn't it be smarter for me to get a few more books on my resume before I start pestering agents?

3. This author has offered to critique my query letter, bless him. After I have the query letter mastered, blah, he suggested I join Publishers Market Place. Is this the best place to start looking for an agent? Do they rate agents, like a five-star hotel?

4. I've really enjoyed working with this small press. They're friendly. They listen, consider my opinion, liked my ideas for the cover, and are generally a joy to work with. Did I really get that bad a deal for a first-time author?

So glad you post these anonymously. You're going to slaughter me slowly, if for no other reason than suggesting I could do your job with absolutely no negotiating experience.

Regards,

Shark Bait.

Let's start with A-C  in your initial offering:

A. The author seems like he's going out of his way to make you feel bad: did you ask for this analysis? Did he just offer it up?  I ask because making sure you tell a new author about the vagaries and foibles of publishing without prompting seems particularly callous.  Yes, publishing is a tough industry, and toughest on the people it needs most (authors) but there's no need to rub someone's face in the muck.

B. I'm not sure why Mr. Expert said this. Your royalty rate is a fixed percentage.  If it's 10% of net sales, then it's 10% of the amount the publisher receives, less certain costs (a definition of net sales
should be in your contract.)  It sounds like what Mr. Expert is trying to tell you is your percentage of net sales will convert to a percentage of retail or catalog price.  So fucking what? If you're happy with your rate, that's all that counts.  Could an agent do better for you? Most likely, but it's too late now
and Mr. Fucking Expert KNOWS THAT.

C. An advance is NOT a loan. It's an advance against royalties. Loan means you have to pay it back. You don't have to pay back an advance if the book doesn't earn enough to cover it.  And giving an advance is NO guarantee of a publisher's efforts. Trust me on this.

Now to your questions:

1. This author has won Leftys, a Nero, and a Shamus. Does the publisher submit their authors for these awards, or does their agent?

You can look up the submission guidelines for each of these awards.  If the publisher can submit books, they should. Make sure you email your publisher with plenty of time for the books to be sent.
If the publisher won't do it, you should (if the awards allow it.)  A lot of these awards have guidelines on who is eligible. Read them carefully.

2. Can I not simply learn from this, and for my next book negotiate a better deal, instead of sharing my meager buck a book with an agent?
Yes,  of course you can negotiate a better deal for yourself. And yes, having an agent is a good idea (what, you think I'm gonna say it isn't??) for lots of things besides the contract. The problem with having a "few books under your belt" before pestering (never EVER use that word in relation to querying even in jest. Respect yourself dammit) querying is that you've also got a sales record now. I hope that will be a plus. Most times it isn't.

3. This author has offered to critique my query letter, bless him. 
Oh good, an author critting a query letter. Is this guy trying to seduce you or something? Ok, that's probably not fair, but I'm having a hard time reconciling how busy I know my clients are with the idea that this guy has a couple spare hours to crit a query.  (And trust me, I know exactly how long
it takes to crit a query! QueryShark anyone?)

The trouble with an author critting your query is that the author isn't sitting on my side of the desk. You're MUCH better off getting help on your query from agents and there are some good places to do that: writers conferences, workshops on queries, QueryShark etc.

3A he suggested I join Publishers Market Place. Is this the best place to start looking for an agent? Do they rate agents, like a five-star hotel?

Publisher's Marketplace lists deals. It doesn't rate agents. If you want info like that, the best place to go is AbsoluteWrite.com 

4. I've really enjoyed working with this small press.
If you're happy with your publication experience don't fuck with it. This is why I'm so leery of Mr. BigShot offering to "help." It doesn't sound like you wanted help, and honestly, it doesn't sound like you need it.

Lots of people are out there offering advice to writers. Hell, I do so right here on this blog. Don't listen blindly. Measure what you hear and read against your own experience and judgement. Things like where to put an address on a query letter are techniques and you can employ them or not.  Things like "you need an agent" are NOT techniques and one answer is not right for everyone. The fact that I think everyone needs an agent does not make it true.  (That will change when I am QOTKU)

Frankly, ditch Mr. AwardShot and give yourself some well-deserved credit for getting happily published.