If you are a divemaster or above, or involved/sponsored in/by a dive related business or career you can enter, but you'll need to be able to prove it with credentials. I've got a tough enough time getting my wife in, each year they seem to want to see more proof of her involvement in the business, even though we've been going to most of them since '01 or '02. Technically they try to keep anything from being sold on the floor during the show for the most part, but there are usually knick knacks available for carry out purchase... but not lots.
DEMA is more of an informational event if you're not actively buying. The dealers tend to have most or all of their lines shown, whatever they can cram into a 10X10 floor space (more if they purchase more booths) to show to their retail customers and potential retail customers. The show is geared towards stores, not so much looky-lous, and apparently that buyer tag will get you more attention. This will be the first year we'll be wearing buyer tags, been wearing a boat operator tag for years, it'll be interesting if things change for us.
If you're goal is to score a great deal on personal gear, you might be in for a let down. If you want to learn more about the industry, there's opportunity.