So, to be clear: you DON'T HAVE to register as a sole trader, but you DO HAVE to declare any income to the taxman. They will then decide whether or not to pursue you for some tax. Given the nature of these affairs, it is then generally easier to register as a sole trader, and do some shoebox accounting, which should make it very quick to see for the taxman that they are flogging a dead horse.
I think this really only becomes an issue of you do this on a regular basis. Otherwise everybody selling anything on ebay would have to register, too, and that's not happening, is it?
To be honest, I am not too bothered with that side of this debate. And even though Pete seems to think this is serious, I think you'd be able to demonstrated quite easily that they are wasting their time. What I am more bothered about is the fact that you do not value your own time and effort. And your statement about having to charge £18 for a tealight holder does intrinsically validate my comment about professionals being faster.