[roel_v]

Eh, if there is confusion at all, it isn't on my side - it's perfectly possible for there to be a sale without any merchandise.

Why does it matter that there are more shares being traded than that actually exist? It isn't about the actual trades, it's a simple contractual thing - one party promises something, the other agrees to pay for it, and as long as both end up satisfied, that's it. There is no 'merchandise being created from nothing', it's just one party promising to do something, that's it.

"e.g. more shares existing in a company means every share is less valuable"

This doesn't make sense - there are no shares created. There is a party promising to deliver shares, that's completely different.