just the stuff I mentioned previously: the #1 problem with a bike that has sat for a long time is rust in the gas tank, or fuel that has partly turned into jello, then got sucked into the filter, fuel pump, carbs or injectors...
Its a bigger problem with carbs, but can also clog injectors. Take a flash light with you, look inside the gas tank: it should be shiny clean steel and clear gas.
ask the owner how he prepped the bike before he stored it. Sometimes people dont know today will be the last day they will ride the bike for the next 2 years, they pull it in the garage with half a tank of gas.. and thats the way it is two years later when they decide to sell it.
There are some known issues with the 1600/1700 engines. I think the only one that was not fully resolved by 2010 is the way the drive pulley is attached to the engine. They improved it over the years, but its still a single nut on the shaft with a washer that sorta locks in place. If that comes loose (usually from hard compression braking) the output pulley will wobble on its splines, and bugger up the output shaft. Unless you grab the pulley and it wobbles in your hands I think all you can do is ask if he ever had to torque it back down?
On the tires: look at the date code on the sidewalls. Its the only thing that is molded recessed into the rubber. It will say DOT something something then WkYr Wk = week of production from 1 to 52, and Yr = last two digits of the year 20XX. They are most likely the original tires, but maybe the rear was replaced.
BTW, I have a question for you. Since you owned a Venture, I just got a used 2000 royal star. The bike had old fuel in it, I have been running seafoam and it seems to be running solid on all four cylinders, but I have noticed: when Im cruising along just barely cracking the throttle open, the engine is very smooth, no vibration at all. But in 4th or 5th gear, if I really get on it, if I crank the throttle wide open, I can feel the engine pulsing and the bike vibrating as it accelerates. Once the engine is up to higher speeds (like 60 in 4th gear) its not so noticeable.
I know there are no counter balancers in this V4 engine - is that pulsing and vibration under full throttle normal? Im worried that maybe one cylinder is dropping out when Im hitting the main jets hard. Maybe Im expecting the bike to be more balanced (like a gold wing) than it really is? I still have to replace the plugs and air filter, so Im not finished with the full tune up yet.
On my last tank of gas Im getting 51mpg riding on secondary roads, so the engine is running well in general. If anything it might be a bit lean. After I accelerate hard up to any speed, and back off the throttle, its completely smooth again - even at 80mph in 5th gear.