Had a rental car once where the parking brake was essentially nonfunctional - the brake itself was hidden down next to one of the pedals (instead of by the center console) and it was clear that many people had simply attempted to drive off with the brake engaged. This car didn't even have that many miles on it (<20k km, IIRC).
I would definitely avoid buying a rental car unless you're desperate...
It depends. Your common sedans and even SUVs will usually have a stick or button on the center console for the parking brake. Trucks and pickup trucks, buses, vans, and other such "heavy duty" vehicles will more likely have a foot pedal parking brake.
I've seen people drive entire trips with the parking brake engaged because the position the stick/button/pedal/Brake McBrakeface is in isn't always obvious, the parking brakes themselves don't provide any resistance as far as driving is concerned, and they don't know what the car's ringing warnings are and don't care.
Making the parking brake warning scream "PARKING BRAKE!" instead of the generic ringer, if the car has one, will probably go a long way. I know it won't happen of course, because that's a localization expense nobody wants to pay for.
I would definitely avoid buying a rental car unless you're desperate...