Mavven - $275 for the smoker, cart, and cover seems very fair. The extended cover alone sell for around $200. Not sure about the price of the cart. The cover is very high quality and will outlive you. If it were me, I'd offer him $225 and see if he bites. Before finalizing the deal, I'd still want to know the build date and see it in action.
Don't be concerned about the seal. They don't have a seal or gasket, it's metal to metal. The door requires a little effort to close and latch, which is very tight. New units leak a tiny amount of smoke from around the door, but that's normal and not a problem at all. As you continue to use the unit the door leakage reduces then disappears completely.
To answer your question, it's extremely uncomplicated. Probably the simplest cooking tool I've ever used. Open door, put 2 oz.-4 oz. chunks of wood in the holder, put meat on racks, close and latch door, plug it in, set temperature, and go do something else until it's done. Kind of boring, but it works every time.
BTW, not to brag, but I stumbled across a never used 3 year old 009 that I bought for a second home I have in Florida. The sellers wanted $100, but took the $75 I offered. I was driving a sports car and couldn't carry it so they even delivered it to my house about 3 miles away. It was little used and I sold it 3 months ago for $300. Some times you get lucky.