Flat out done selling anything on Ebay or with PayPal

[bobH]

I'm puzzled... Anything I sell, I take a loss on. Be it car, or parts. So, am I supposed to collect/pay tax on something I sell, even though it was taxed when I bought it? For example, I have one vehicle I bought in 2000. I'd like to sell it, and have considered ebay as a means. It was in the 15K range when I bought it, and paid tax on it. It might bring 7 or 8 today. I collect/pay tax on what?
As for 'income', and the IRS, how can it be 'income', when I receive half of what I paid?