I've been thinking about this for a while and came up with some idea of how this could work
Basically an Auction House allows you to sell unwanted items/modules to another player, both the seller and buyer are anonymous throughout, even after the auction is over.
all weapons/sensors/cloaks/cores etc that you can normally 'Buy' are regarded as 'common' equipment.
items you get from NPC drops are considered 'Uncommon'
Artifacts from Missions that can only be completed once before they finish ( I.E the mission that gives you Mass Surface Melters ) are to be considered 'Rare'
there can be a time limit on how long you'll want the item up for auction, up to a maximum of 24 hours.
4 Hours
8 Hours
12 Hours
24 Hours
each time slot has an increasing price which should be 10% of the item you are auctioning
EXAMPLE
Dark Energy Core MK 3 costs 114,000,000 ( not including Minerals )
4 Hours 11,400,000
8 Hours 22,800,000
12 Hours 34,200,000
24 Hours 45,600,000
If the item doesn't sell, you get it back Minus the Auction fee you paid to place it in auction, depending on the time you selected for it to be there.
every item has a 'Base Credits Value' ( BCV ) which is 50 % of its shop value if sold.
Equipment that has Minerals needed to make will be different,
the item itself will still have it's BCV , but the minerals used to buy it will be 20% of their value
the costs are then added together to give a new BCV for the item in question
during the auction, to 'outbid' the highest bidder, you need to increase the bid by 5% or more.
at the end of the auction, the winner gets the item in question and the seller gets his credits.
When you place a bid, the credits you have placed are 'Locked' until the auction is over, or you are out bid'
sub notes.
Common Items can only go as far as 25% more than the BCV and the seller gets 100% of the Credits bid for the item
EXAMPLE
Dark Energy Core MK 3 costs 114,000,000 + minerals at 20% value ( 10,794,454 ) = 124,794,454
+ 25% ( 31,198,613) = 155,993,067 - this is what the seller receives. any other bid past this figure will be lost.
Uncommon Items are the Same except the Auction House Keeps 10% of the winning Bid( and everything past the extra 25%), the rest is passed onto the Seller
Example-
Dark Energy Core MK 3 costs 114,000,000 + minerals at 20% value ( 10,794,454 ) = 124,794,454
+ 25% ( 31,198,613) = 155,993,067 - this is what the seller receives. any other bid passed this figure will be lost.
Lets say the final bid was 187,678,245 the auction house keeps 31,685,178 as that is passed the 25% mark bringing the figure back down to 155,993,067, the auction house then takes 10% of this ( 15,599,306 ) giving a total of 140,393,761, which is what the seller receives for the item
RARE ITEMS
these are of exception, they can go up as far as twice their BCV, however the Auction House keeps 30% of the winning bid and everything passed double the items' BCV
I shouldn't need to provide an example here, as from above you should be able to see the process by which this goes

reasons why i thought of this, as while browsing the forums i come across many threads that are either selling tech parts for Credits/TM/EM etc or planets for credits and a multitude of other items
Im open to changes to this and other alternate ideas to improve it, let me know what you think and please give 'constructive criticism' none of this 'that's a stupid idea' crap

EDIT- forgot to note that artifacts pulled from arti shipments are/should also be considered 'common' in the sense that you can never run out of artifact points