Wow, so much going on with this thread.
First of all, OP, I am very sorry to hear of your experience. Some of the things I will say may not be nice, nor is my intention to hurt you.
I was in hard times many years ago and bought macbooks and sold them. I always required money orders of cashiers checks. (This was before Ebay and pay pal) One time I sold it to someone I had an uneasy feeling about. I thought I was being prejudice and got mad at myself about that. But turns out the guy gave me an altered money order and I was SOL....till I found out my home owners insurance covered it and it was called "Theft by Deception."
Now the next thing is I have a problem with your and many posters here thinking that the buyer is guilty. Maybe he did not receive the package. There is no way to control that unless you have a signature requirement. Many times I come home and packages are just sitting by the door. So maybe your buyer did not get their package.
I have sold many items on Ebay. I find it the best way to sell most of my stuff. I ALWAYS require the buyer to buy the extras on expensive items. That way both the buyer and seller are protected. That's another reason I would only use paypal. It protects both parties. Also, don't let a buyer make you send something out when you can't send it out properly, ie: going to the PO when it is open and get a delivery conformation and signature form. For the future, you can also use UPS from Staples. They are open late and you can get it done there. Remember, charge for this when selling an item.
Next thing, DON'T EVER let anything go into collections. It really hurts your credit. If the OP would loose a job or his wife finds a new one, today, many employers will pull your credit report. The last thing they want to see is low scores and collection accounts.
So in closing, a lot of mistakes were done with this transaction. It sounds like it was an expensive lesson. Next time protect yourself. i hope things turn around for you and your wife. One day, may you look at this as a well learned lesson.