I've you haven't had a Passat before, they're all pretty unreliable compared to a Japanese car. More precisely, you have to be absolutely scrupulous with maintenance or very bad and expensive things will happen.
However, it appears the one you've chosen is a good example. First, make sure the timing belt has been done. It's not technically due by miles, but it's WAY past due by time. As preventative maintenance, it's a $1200 job, but if it breaks, it's a $4000+ repair. Next, make absolutely sure the heater core isn't clogged and that everything electrical works. Then inspect the front suspension for looseness and rattles. All good? Buy it.
Oh, and don't believe the seller if the Check Engine light is on and he tells you it's nothing. Maybe; but it could also be the dreaded catalytic converter problem the V6 suffers from - and that could be another $2500 or so.