Sharp 10,500 BTU Portable Air Conditioner

I bought this awesome portable air conditioner from Costco brand new last year to use for the game room above my garage which got hotter than the rest of my house. And then about a month later, I ended up replacing my entire furnace and A/C system in my house anyway and didn`t need it anymore.
This thing is wonderful. It cools fast, purifies the air, dehumidifies and even has a timer on it. It has three air flow speeds plus a max A/C setting. It has a sleep setting that will adjust the temp after a set period of time so it doesn`t remain as cold all night long. It has wheels on the bottom so you could easily move it from one room to another if you needed to.
The blower is considered "library quiet" and I never had any issues with it. It does need to be "vented" to a window but comes with the attachment as seen in the picture. I also have the remote which has an LCD display (and I may still have the manual too) for it.
This item is basically brand new. I could return it to Costco since their return policy is dynamite but feel like it`s not the right thing to do since I did use it for a month.
$350 for this is a steal so please don`t low ball me.