Carbureted bikes may need a little time to warm up in order to hold idle without dying. A clean and tune should fix that, but that's effort the owner may not be in a position to make for whatever reason.

However, all you need to do is hold the throttle at, say, 1500 RPM instead of 1000. Enough to not die. Adding a cheap throttle lock makes it so you don't even have to stand there while it warms up.

There is zero reason to rev a bike in neutral, at any time, besides dick swinging.