I suppose you are familiar with the market so I won´t go in detail how the market works.
If you need explanations check this out -->Market Guide
Note: The main reason why I´m writing this guide is because I think some players don´t know how to sell their stuff w/o destroying the market. Read "Keeping the market profitable" to see what I mean. I will expand this guide soon and will add strategies how to make profit in MO :)
Every good MMORPG has an economic system in which you can trade and make profit, and so does RPG MO. Usually the Economy is regulated by supply and demand. If an item is in high demand but hard to get, people tend to pay a lot for it. The other way around, if the item is easy to get and the market is full of it, it won´t reach such a high price. To make profit it is recommended to buy low and sell high. These are the very basics of trading and probably no news for you.
Keeping the market profitable Edit
To make sure your items will find a buyer, you have to keep an eye on your sell offers. Do it as often as you can so your stuff will always be the cheapest in market. However, sometimes it´s not needed/good to undercut your "opponents" price, e.g. if the price is already at rock bottom. But IF you undercut the price there´s a very supreme rule: Never undercut the price in large steps! It is pretty unwise to undercut an item what´s worth 100k in 1k steps or more. Doing this will make the price fall into senselessness in no time. (picture below shows an example of how not to trade) It really doesn´t matter if you underbid in 1k steps or in 1 coin steps. People will ALWAYS prefer the cheaper one, even it is only a difference of a single coin. Keep that in mind and your item of interest will stay tradable.