Hi
Because the Auction/Market currently runs on different software to the Forum, it requires a separate registration. Also, because a trading account requires (like ebay) more personal details from members than the Forum (i.e. home address and phone number), it's not possible to simply link the two accounts.
In your case, I notice that your Auction/Market Username is Glitteringprize67, without the hyphen, but your password is identical. This is because the Auction/Market software does not accept non-word characters. Confusing, I know.
I'm currently redesigning the site to overcome this, although the requirement for more personal details to be registered will of course remain.
When advertising, if you don't make it very clear what you're selling, you're bound to run into trouble. I think your ebay advert
conveyor an old beautiful machine "converted to new 10p.size" which fails to mention it was scratch-built long after decimalization, is potentially misleading. If somebody bid £800 believing they were buying a vintage collectible, would you call them a "time waster" if they subsequently refused to pay?