I just purchased the game a couple of days ago, it came with all 5 expansions but no manual, so how does the marketplace work? Lets say a monster drops a sword, how do you know how much to sell it for? Or if you are looking for a certain item, how do you know how much it is worth so you don't get ripped off? With an auction house you can quickly see what things are going for and then post a price for your wares but this game doesn't have an auction house so how do you know what a fair price is whether you are buying or selling?
Thats up to you to learn the market price for it, more or less, your work.
I can say this much thought, there is no market for NG, and there is a tiny market for top D grade, above there there is a market thought, but don't expect to get drops like that :P
If you want to buy/sell stuff you need to go to Dion, Giran.
lol you have to look around and research in private shops in towns like dion (for items roughly lvl 20-40 - D grade) and giran (for items of lvl 40+ - C grade and up)
towns like gludio and gludin have most of your NG stuff (sub lvl 20)
It's a good thing - the market is an actually large part of the game in Lineage II, and it gets quite fun after you get used to it - tallying up your earnings, making some calculations, spending time in town for your gear makes it feel infinitely more worthwhile.