Welcome to the Vulcan madness.
A quick check of the charging system is to hold your hand in front of the headlight while reving the engine from idle up to 4-5K rpm. It should brighten as the revs increase.
If you have a meter, voltage at the battery terminals should rise from 12.5+ volts at idle to 14.5-15 Volts at 4-5K rpm.
The vn750 design requires the engine to be pulled from the frame for a stator/alternator replacement. That is a $1000-1200 bill at the dealer.
(However TuxedoSeven has now provided us with a $20 case mod that allows the stator to be changed with the engine still installed in the bike.)
The wimpy 5mm shift tie rod inside the engine cases was superseded with a heavier duty (8mm) one beginning with the 1991 models.
The 6 rubber and plastic crankshaft balancer dampers are items that can be expected to start deteriorating on a bike of this age, especially if it has sat for long periods without being ridden at all.
Rear spline failure is also a possibility if they have not been lubed properly.
I am not trying to dissuade you from buying this bike, as mine is the same year with only a few more miles on it, and runs perfectly.
I am just providing you with some ammo for dealing points in trying to talk the dealers price down.