There are currently four regular types of vendor in the game:
There are also currently two special types of vendor:
All of these vendors have fixed prices, not depending on supply and demand.
Regular Vendors Edit
At regular vendors the player may purchase or sell items. To do so, walk up to the vendor NPC and press [T] to "use". The vendor window will pop up.
You may sell any item in your backpack by right-clicking it.
You may buy any item available from the vendor by right-clicking it in the vendor window, provided you have enough credits and meet the requirements regarding necessary trainings and level. If you don't meet the requirements, the item is marked in red.
In case you accidently sold an item you didn't intend to sell you may buy it back by clicking the "Recently sold" tab at the bottom center of the vendor window.
You can buy ammunition from every regular vendor in the game.
Vendors buy items for a quarter of the normal price, rounded down. The minimum price per item is 1. So Consumer Grade Micromech sells for 6 (25 / 4 = 6.25), while Spore Micromech sells for 1 (3 / 4 = 0.75).
The prices for vendor-sold weapons are generally based on a simple formula: Price = Level * Tier * 50 where "tier" is the tier of the weapon training. Thus a level 20 pistol costs 20 * 1 (recruit) * 50 = 1000. Tools also tend to follow this pattern (as tier 2 weapons), but there are exceptions.
Armor is a bit more complex. Different locations have different factors, and the multiplier is (level+4) instead of just level. The full set of factors is listed in the table below. If we consider hands "stage 1" armor and torso "stage 5", the raw formula is (Level+4) * (Tier+3) * 1.25 * (Stage+1)
Special Vendors Edit
The other major difference is that you cannot sell items to these vendors, nor can they repair items for you.
Vendor list Edit
For a list of vendors, see either the articles of the above mentioned vendor types, or see Category:Service NPCs.