[Majost]

Actually, I think it's in your favor that it's a check... You can choose not to cash it. They won't be out any money, and you won't be in trouble with the law or the Canadian equivalent of the IRS. Just tell the first buyer that they sent you a check, not a money order as agreed, and that the deal is off.

Rip up the check, and if they contact you any further, just tell them to find another sucker. And really, if you do this, you've done nothing wrong, and you can get the police involved if it gets any messier.

Don't think about the money. Don't even look at the check. Just rip it up and move on with life.