Okay, first I need to perpend the disclaimer that I am one of those horrid people who voice opinions purely on what they have read on these forums; I am not in the beta, in fact, I've stopped applying since at this point I'd rather just get the game when it comes out.
That being said, I am also aware that most of the negativity about the Retainer system as is are not the type of people who enjoy micro-economic management on the player side, but I will give this a shot anyway.
I am actually of the opinion that, on paper, the retainer system as is has a lot of potential. It just does not, and cannot, work in a beta. As I see it, this system gives DoH and DoL in particular a huge arena to do battle, much like the DoW and DoMs do battle in the fields outside. Over the course of the first few months, certain crafters and gatherers will establish themselves as leaders in their field, and give rise to the "Buy from the guy on the third corner from the left, he always has good deals" phenomenon. Savvy buyers will look beyond the big name Retainers and search out the "mom and pop" retainers, more specialized, but often at a cheaper price. You can name your retainer, leading to brand naming.
Another thing that could come out of it is middlemen. In the case you don't want to deal with getting your retainer noticed in the crush, find one of the big name sellers and sell him your stuff, I'm sure he'll be willing to mark it up a bit and put in on his retainer. Even better would be when several people get together and cooperate, forming a conglomerate, all selling out of one Retainer, increasing each's profit margin.
What Square Enix needs to add to make it work this way isn't a search function, it's an advertisement function. People need to be able to put themselves out there in the public preview. Adding a search function would make it easy, but it would completely destroy what I see is potentially a very rich and complex market. That being said, I would be happy with a search function if that is what Square Enix decides to do, but it would no longer be any more visionary than an AH, just one where you actually walk around instead of looking at a vendor window.
I would like to reiterate that I am very well aware that complex economy systems are not something everyone enjoys, some people just like crafting, some just like combat. I'm just saying that this system by the sounds of it isn't all bad, it just hasn't had a chance to grow yet. I haven't even talked about people who could make gil just by playing the trading game, but I image that one is pretty self evident, and boring to most people besides.
Unfortunately, it's impossible to know if it would work out, since by virtue of it's very deesign, it would take months of perpetual servers (i.e. no character wipes) for the market to settle correctly. Not to mention that in the beta, players don't have the same levels of self interest to actually advertise.
I'll help shed some light on this.
The retainer system is actually pretty interesting, as you can set up retainers (and personal bazaars) to both sell stuff AND buy stuff, this allows you to play kind of a trading game where you buy one thing, do a bunch of trades through bazaars, and come out with what you need if you can play the game well.
What's missing right now is a robust searching tool, the sheer number of retainers sitting in any given marketplace is absolutely appalling and completely unworkable with no way to search them easily (there's also a ton of lag in there but they've already acknowledged that).
Unfortunately I don't think advertisements on bazaars are necessarily the way to go in light of the following: http://vnmedia.ign.com/l2vault.ign.com/images/FaultyScreenie/10-28-2008-faulty-screenie.jpg
That's from Lineage 2.. Aion had a very similar problem for a while.
I do agree that certain individuals will become known for certain products at certain prices and that will take shape organically on its own once the retail game hits.