I've got a pretty good idea of which project I want, and so I'm wondering how essential it is to have a buying agent. I'm pretty good with legal documents, financing and small print.
In particular, will the seller provide a discount to offset the buying agent commission?
Agent's are generally quite useless, but particularly so in this type of situation. They are no better able to look over floorplans than you are. And as long as you are moderately intelligent, you should be able to go over the purchase agreement (and of course, your lawyer will go over it in greater detail).
They might convince you they know some extra tricks about which suites are "dog" suites for example, but really all they're gonna tell you is don't buy a unit close to an elevator or garbage chute. Go and check out the site for yourself to get an idea of which views will be the best, and which will be obstructed. Any tips they give you to make a unit more desireable for resale later on are usually very obvious (ie get a parking spot), and nothing you wouldn't be able to figure out yourself.
That being said, some developers may not offer you any additional incentive to buy without an agent. Go into the sales center, make up some name when you sign in, and then tactfully tell the salesperson you are serious about buying, and are looking for free upgrades or cash discounts for purchasing without an agent. Make sure you do this after you have seen the prices and any incentives they already have going on.
Projects that have been for sale for a while usually will offer you something. Decide whether or not it's worth it. If it isn't, or if they aren't offering you anything at all, find a friend or family member who is an agent and get them to go back and buy it with you. Since they really aren't doing any work whatsoever, make sure you tell them in advance that you will be expecting the majority of their commission. Offer to pay them a few bucks for their time (ie a few hundred dollars).
Agents are a dime a dozen, and you almost certainly know someone who is, or at the very least, a friend of a friend. Considering they are doing virtually no work besides showing up with you to the sales center, you should be able to find one who will oblige.
This is the advice I always give. Recently, a friend was able to get a few free upgrades at a unit in liberty village for showing up without an agent. Another friend of mine who bought a newer unit downtown had a seller who would not budge, so she gave her agent friend $500 and pocketed the rest of the commission herself.