I've been using Agon for some time. Some information would be handy to aid your sale:
What is the retail value of the piece? Looking at the website, it looks like the "standard" model is $1,000. There's no "extreme" moniker with add-on price shown. I assume there are extras that would add price and value.
If it was back at the shop, what was done?
How do you expect to be paid?
For a piece in basically "mint" condition, under a year old, expect about 1/3 of the value to be gone. This figure varies, depending on supply/demand. For future reference, for items not in pristine condition and/or over a year old, you probably are looking at a reduction of at least 1/2 the original price.
You may want to consider posting an ad on Agon, where it will get WAY more exposure than here.
Good luck!