To add another point of view;
The rules as they they stand are generally clear enough.
The issue of whether an item is being sold commercially could do with some clarification and reassessment.
The consensus here seems to be that it would be useful and fair if people can sell surplus kit and materials to the benefit of the membership, IF the items offered aren't their primary business products.
Hence timber merchants should pay to advertise wood, turning blanks etc, through the premier post scheme, but a joiner could sell some surplus hardwood left over from a job. Similarly a secondhand tool vendor should pay to advertise, but a kitchen fitter could sell on a tool he was upgrading.
The issue of VAT in these circumstances is quite straightforward, all prices advertised must be the prices paid including VAT if chargeable. A courtesy would be to expect people to add to their listing if a VAT receipt will be issued for the sale price.
The reality is that this is already happening in the 'For sale' section to an extent. Smart moderators would legitimise this, rather than just overlook it which can cause problems when later disputes happen with other potential vendors.