I did test ride before buying. Local sale, private party, the bike was 7 years old at the time.
I came, talked it over with the guy, and then after discussing some basics, I asked if he'd be okay with me going around the neighborhood for a bit. If he had said no I would probably have walked away, but it's a case-by-case thing.
Having lived in NYC before this, I'd be a little nervous in traffic with a bike I couldn't flat foot that is as top-heavy as the Wee feels to me, but it's your call.
Definitely sit on it in a showroom, and see if you can imagine it with 5 gallons of gas in addition to the weight you feel... I'm 6'3", I can flat foot it fine and I still sometimes find it tough to maneuver on a duck walk, or pushing alongside.
"Never run out of real estate, traction and ideas at the same time." - Mario Andretti