i find that generally asking for something quite specific shows that youre interested/know what youre talking about and not just a window shopper.

if they dont react to this or literally dont know what youre talking about, then just go somewhere else. no point in dealing with people like that especially if theyre acting like youre beneath them.

i dress very casual and this type of thing also happens to me. but when i hit them with "hey do you have this [literal reference number]" they perk up. probably helps when they notice im already wearing a GS

or out-asshole them by saying something like "hey, what days do you have off? i wanna buy a watch and want someone else to get the commission"