No, it's not dust. It's imperfections in the machining of the bracelet end links. But it might not be a reason to refuse the piece just based on that. I don't believe this is a particularly high end rep, yes it might have a 7750 movement in it which attributes to the cost, but the casing is all dependant on the factory.
You could send a polite email to the dealer asking if all the end links are a bit rough on the edges or if it could be replaced for a better one.
He might come back and say that they are all like that, in which case it's just the rep itself and not the particular piece that he has chosen for you.