You should be taking some time during the,prebuy so you could turn on the,water heater and at least have warm water in 15-20 minutes. Turn that source on and turn on the other... if lp and electric... and by the time you are finishing up your prebuy the water should be hot proving that the second source is also working. Turn on the ac and if it isn’t putting out cooled air within minutes it needs working on. The frig... I’m not sure as mine runs 24/7/365 so I’ll not comment on it.
If your prebuy inspection doesn’t take long enough for testing the water heater it is too short.
This from a buyer who bought his last rig sight unseen. ;)
