Hey there!
So I heard you wanted to make an auction.
Hold on for a minute, there is a few things you need to know before you start.

1. LABEL YOUR THREAD TITLE
When you make an auction, always label your thread beforehand.
Lets say I am trying to sell an Aqua Force, I would label my thread as;
[A]Aqua Force or [Auction]Aqua Force.
This lets people know that it is an auction rather then a sale or a quick buy.

2. STARTING PRICE
All auctions need a starting price, make sure you set yours as at a reasonable level, or else no one will bid.
Keep in mind that starting price should be lower then the amount that you want for your item.

3. MIN RAISE
The minimum raise is the smallest amount someone can bid on your item.
Always try to make it reasonable, again, or else people will bid stupid amounts and you won't make any TC.

4. END DATE
This might be one of the most important rules, but all auctions require an end-date.
Otherwise, there will be no winner and the auction could go on indefinitely.

5. AUTO BUY
The auto buy is the price someone can pay for your item without having to bid on it.
It is always a good idea to make your auto buy more expensive then you think your item is worth, so just in case someone doesn't want to bid they can buy it right away.

6. RESEARCH
Make sure you research how much your item is worth before you plan on auctioning it.
An auction that is severely overpriced or underpriced because of not researching will go well for no one involved.

7. USE COMMON SENSE
Even if you follow all these rules, it is still probably a good idea to use common sense.
Attractive, concise, and neat auctions will probably do better then CAPSLOCK and smiley spam.

WARNING:
KEEP IN MIND THAT RULES 1-6 ARE ALL REQUIRED FOR ALL AUCTIONS
COMMON SENSE IS NOT REQUIRED BUT IS SEVERELY RECOMMENDED

Example:

Thread Title: [A]Aqua Force
Starting Price: 500 tc
Min Raise: 200 tc
End-date: 24 hours after last bid.
Auto Buy: 5k

Now that you know how to create an auction thread, go off and sell to your hearts content.
:V

This could help too

You again with your common sense :P

Remember that auctions also involves texture sets and such things, so adding the name of the person that made the set, disclaimers and so on needs to be added to this tutorial I guess.

also flames (forgers, no template screenshots etc)

Easily the best tutorial out there. Most informative, +rep.

Nice tutorial here, bro! +rep'd ofc.
Btw, i know that since waaay older times

Yours is better than this one, and much broader, so I won't close this. I'll still link this in the thread though.

Very nice, steve.
+rep