Here`s a check list from the Vulcan verses.
Check the charging system as KM suggests. At one time I would have agreed with him to walk away if the system wasn`t charging.
It used to require an expensive (in your time or shop labor costs) engine pull to replace the stator/alternator.
It doesn`t have to anymore.
There is an inexpensive and relatively simple engine case modification that many owner/riders can do themselves now.
If you like the bike other than a poor charging system, tell them it will cost at least $1000 to repair at the shop (that is true), and bargain the price down. If you do the work yourself, the stator can be replaced in less than a day for under $200, using the mod outlined above.
Get any maintenance and repair records the seller has.
Ask if the rear splines between the driveshaft and final drive have been lubed with high moly lube like Honda Moly60.
(They won`t know, but it gives you another bargaining point.) It needs to be done every 10K miles.
Many bikes left the factory with no lube on the rear splines. Check them asap.
Do it yourself when the rear tire is changed, or do it now if there is a new tire already on the bike.
Check the age of the tires:
If the bike still has a conventional wet cell battery with 6 caps on top, it should have an overflow hose going down near the ground.
Check the frame under the battery for any acid spillage,damage/corrosion.
If there is any significant corrosion here, I would walk away from it.
If it looks good, you will still want to change the battery out for a MF-AGM battery sooner rather than later. Another $60-80
You will want to change out to NGK DPR7EIX-9 Iridium spark plugs too, after experienceing a few hard stars, cold and hot. 4 plugs @ $7-10 each
This may seem a bit overwhelming, or like the bike has a lot of problems. It doesn`t have anymore problems or weaknesses than any other 10 YO motorcycle.
When you take it for the first ride you will fall in love with this powerful midsized cruiser. Good luck with the hunt for a scoot.