Many people create 'toons strictly for the purpose of bazaar trading. There may be people who disapprove of it, but since SoE has made it very easy to transfer items between one character and the next on the same account, I'd have to say there's nothing really wrong about it. It's not truly NECESSARY though...while in the bazaar weight seems to mean practically nothing (which is good because plat in large quantities weighs a LOT, and some of those spells that the fragile casters need can cost plat in very large quantities indeed.)
People not flagged as trader yet facing the wall maybe be too lazy to flag themselves afk, or they may be searching for something using the /bazaar command. Even using the sorting filters, it can take quite some time to find the best upgrade for your plat. Or they may be trying to sell through /auction or /ooc ... particularly if the bazaar has reached it's limit of traders, or if they only have a couple items to sell and don't want to bother setting up as a trader.
As for special things to know about the bazaar: It currently has a limit of 550 traders...which it often reaches in the wee hours of the morning when people decide to leave their traders up overnight and hopefully wake up to some extra plat. Prices fluctuate rapidly, depending on how many people are selling an item, how fast someone wants to sell the item, and how common the item is. Common items such as spider silks tend to have a fairly stable price, whereas ornate armor molds/patterns have prices that seem to vary by the hour, and sometimes by the 10's of thousands of plat. At night prices tend to be relatively lower than in the daytime...as people setting up to trade overnight are likely to undercut the lowest current price. There are far fewer traders during the day, and more people shopping, so prices tend to be higher during the day.
Oh yes...and don't forget to put your trader sacks back in the bank before you leave the bazaar....they weigh a LOT and I've seen people get stuck once they zone out with all that weight on them.