I rode in our 19-foot Bambi after installing 16-inch wheels, Michelin XPS Ribs and Centramatics, to check out the ride. It was about the same as riding in our newer model Tundra CrewMax. While I didn't notice anything unusual in my 5 minute ride, I suspect that bad brakes, worn-out brake shoes, bad wheel bearings, bad axle or bad shocks might be detectable during a test ride. Also, poorly hung cabinets, defective door latches and loose things like the air conditioner would probably be pretty obvious.
While I definitely wouldn't ride back there for more than a couple of miles, I wouldn't hesitate to ask for a test ride when buying a used trailer. After all, would you buy a used car without taking a ride in it?
By the way, my wife and I picked a familiar, straight stretch of country road with almost no traffic, and known pullouts where we started and stopped. And, we were in constant contact with each other via cell phone.