Selling my friend's used items on Ebay

Q1. I'm selling my friend's personal guitars through my ebay account. If I sell it for $1000 and he tells me I keep $200 for commission and I issue him an $800 check. I still get the full 1099-K for the $1000 sale from ebay. How do I account for this in my taxes?

 

Q2. What about selling my used personal items for less than what I originally paid for? If they add up to the 1099-K threshold, how should I report it?

 

By the way, I don't consider this as a business. I just happened to have been using Ebay for a while as a buyer and a seller, and my friend didn't want to bother creating an account for himself to list his own stuff.

 

Thanks.