The humble exhibition is going to become priced out of existence. As an exhibitor, already are often expected to take the cost of including tagged leads into account when bringing along a display (something I've normally found quite useless, given I've never heard of the actual layouts internal wiring getting a check, which is where there is more likely to be electrical issues floating around, not with a store bought cable or power board).
Anyone who thinks that Test & Tag is just about purchased power boards & extension leads, has the wrong information. All mains powered equipment should be T&T too and in advance of the event. While some clubs MAY offer such a service at the set up time, the problem is what happens if a key part of a layout fails the test? That component CANNOT be allowed to be plugged in, until the fault rectified or replaced. Much better to be prepared, so that your soldering iron or lighting pelmet or whatever complies, BEFORE it leaves its normal place of residence.
As someone who does T&T for my club, I have found a number of faults with club equipment from time to time. Common problems are faulty power boards (high resistance within the conductors - one tested 17 ohms in the Earth path pin to sockets, compared to the maximum allowable of 2 ohms. This could prevent circuit breakers from tripping!), other problems are wires loose in plug - cable clamp missing, being very common. These are usually caused by pulling on the cable, accidentally or otherwise. Computer leads, IEC type are another - I was speaking to a professional T&T man & he told me that he's found a number that have had the active & neutral reversed, a definite no, no.
So factory made equipment can be supplied & do go faulty.