The Market: Confusion

[Atoli]

Like Arecia said, many consider glamour the true endgame. The fact that the materials for that lvl 1 glamour gear are usually incredibly hard to get at release of the recipe (and need a fully leveled+geared crafter) means that isn't just in the mind of the players either, it actually IS an endgame activity. Luckily, some patches later it usually eases up, especially since Palace of the Dead got released we now can get nearly all formerly hard to make glamour gear from there, dropping the price on the market board significantly.
The ones that are still expensive are those that are not yet obtainable that way so people still have to make them the old-fashioned way^^

Other than that, you can also use ANY gear for your glamour needs, not just the gear that is specifically for glamouring. So if you have a nice set of boots for, let's say lvl 35, just normal combat boots that look great though, you can glamour those as well, not just the lvl 1 ones that have no stats^^

As for things to look out for:
If an item is fairly expensive in your book, look it up online to see if 1) it is not maybe available somewhere else (because players often do sell gear that NPCs also sell for a way higher price)
and 2) to check which materials and crafting level are needed for it. If it is easy to make and the mats are cheap but it is still sold for a crazy price, someone is trying to make money off of those that do just accept any price.

What is also helpful is the sale history, that little circle with several horizontal lines in it in the upper right corner of the window in which the various sellers of the item you want are listed.
It shows for how much the last 20 people bought said item. If they all paid 5k and now the only one available is 500k, chances are, the price will soon become normal again so put it on your wishlist and wait^^
(but sometimes, the price just goes up from there if the item is no longer relevant and barely anyone crafts it, or if the materials for it are limited, like for example from seasonal events, or from content no one runs anymore, like Diadem, so in that case, the price may just keep rising and rising).

Also, just in general, it is a player-driven community. Supply and demand are everything. If there is something incredibly rare, people are willing to pay crazy sums for it.
For example, the falcon minion went for 120 million(!) Gil a few weeks back. If someone is willing to pay that much and the item is rare, it is not surprising the seller puts it up for that kind of price.

[Niwashi]

... incredibly hard to get at release of the recipe ... Luckily, some patches later it usually eases up ... dropping the price on the market board significantly.

This is actually one of the possible reasons why you'll sometimes see wildly different prices for the same item. Somebody put it up for sale back when it was still new and rare (and therefore very expensive), but it didn't sell right away and after a while it became more widely available, so the normal price dropped dramatically. If that earlier seller doesn't go back and update their price, their MB posting will be left there still listed at what's now an exorbitant price. They may have chosen that price back when it was the going rate.

(I think I have a couple leftover postings like that, actually. Maybe one of these days I'll get around to fixing them.)