People wheel and deal watches as a living. Just look at most of those watch YouTube channels and they are mostly jewellers who buy and sell. Even my favourite watch channel that British guy who does closeups of high end watches are just a bunch of resellers.
As for the datejust, I think the bubbles burst right now and the inventory is recovering. A few months ago there was a wait list for most models. Dj included. But now i think only a few choice pieces are on a wait list. Supply is catching up to demand.