The following assumes that you already have (or will have) inspected the bike for other issues like signs the bike has been in a tip-over or a crash, and you are satisfied with what you found (or didn't find).
The "big" issue with this bike is that a lot of them apparently left the factory with the rear drive splines pretty much unlubed (as the others above have already mentioned).
This is NOT a design defect, but rather a quality control oversight on the assy line.
These splines, and those in the rear wheel hub, should be lubed with a high-moly grease (such as Honda's "moly 60"...or one of its competitors). Regular axle grease really won't cut it here.
Follow and study the fergy link given above by "OlHossCanada". This will later save you from having to replace the final drive unit, which can easily run several hundred dollars (not to mention leaving you stranded with your bike-- possibly in the middle of nowhere!).
You might take both the side covers off with a coin (they're beneath the seat), and inspect the bike's frame underneath the battery box. If you see where battery acid has attacked (and corroded) the bike's frame--don't walk, run away from the bike. This problem is NOT FIXABLE on any practical level.
Ask the dealer if the bike's tool kit is included with the bike (like maybe in the storage area lockbox behind the short sissybar). This tool kit includes a special socket that makes it easy for you to change out the spark plugs (regular sockets won't fit, as the openings in the cylinder heads are tapered--the tool kit socket matches this same taper).
As JM suggested above, use a voltmeter on the battery terminals and check the voltage readings at various engine rpm's (2k, 3k, 4k). All should read above 12.8--and below 15.2. Readings outside this range suggest the bike's charging system is due for major work--& $$$$$$$$$$.
Be sure and test ride the bike, b4 buying it. Make sure it starts & idles smoothly (with and without the choke), and accelerates strong, without hiccups or hesitation. If you don't check for this, the bike may need a thorough carb cleaning that you'll have to do yourself, later. Before the test ride, inspect the tires for any dryrotting, and proper tire pressures. The factory tires should read about 30 psi cold, front and rear, before you ride off on the bike. Make sure the oil, brake and coolant fluid levels are ok b4 the test ride, as well.
Note that a little bit of exhaust backfiring when shifting gears on this bike is actually normal--but a lot IS NOT.
Work the locks on both the gas cap and the rear lockbox--make sure these locks work smoothly (and that the lockbox closes and opens without problems). With the gas cap open, look inside the fuel tank and see if you see signs of rust (like on the bottom of the filler neck). If you see rust in the tank, you might consider walking away.
On a bike with mileage that low, if either of the exhaust pipes are turning blue next to the engine, that's a sign the carb for the affected cylinder needs adjusting.
This bike originally came with 2
keys--and also ask for the owner's manual.
These are special bikes, because they were the last of their kind. No one else is making cruisers like this anymore--at any price! Ride safe...