Such watches of such values , i would not buy on internet - even if he photgraphs the watch with the right serial number and the correct date and so on and on:
what's the point of selling a 4K watch for 400 dollars? why not 1000 dollars? would still be a bargain, right? So it's like 100% sure, that he might have the correct watch, and pictures,
but will take the money and send you just nothing. And he probably knows, that if you pay 400 euros and get nothing, or a cheap rep, you will not be make a move as it will be far
more expensive to take a laywer and will eat up month of time to get that money back - so i think he just speculates, that you will just let it be.