I don't believe there are any rules about selling either. I've seen hoards of both for sale at car boot sales over the years.
The general guidance is that you shouldn't buy a child's car seat secondhand, as it might have been involved in an accident and therefore not be safe. However plenty of people do and its their risk. It's no different to selling through Trade It or something to a car boot sale.
In terms of an electrical item, if somebody is prepared to buy it without seeing it working it's their risk as to whether it works or not. If it doesn't, they're not going to be able to track you down