To know how to sell something for lots of money, learn from the pros at eBay. Look up COMPLETED offers for 'xbox 360' and open about 20-40 offers.

Notice the view counts and how that compares with the titles.
Bottom line lesson:

'L@@K Awesome 80 account SAFE' isn't going to sell.
'LV 80 Mage, 5/5 T12 raid gear, original own' will sell.

Next, notice the descriptions and the selling prices. Open offers which sold for the most... then view some offers that sold the SAME thing for much lower (or which didn't even sell at all)

Bottom line lesson:

A highly detailed offer has more selling power. Especially with professional sounding guarantees and smalltext. Those top eBay sellers know what they're doing. You'll also notice here that their feedback really helps their selling power as well. So be sure to start gathering some feedback for yourself. It's worth money.

A poorly detailed offer has pretty low selling power.

In most forums, you can sort threads by 'view count' and by 'replies'. Do this and you'll learn how to make a hot offer.