Apart from looks, weight could tell the truth. By the way, some say BMW OEM rims are quite heavy (heavier than replica?). Yet BMW claims OEM should only bend when replica breaks, increasing survival chances.
If weight comparison is not available, you can go
this path. And/or take a wider look at both OEM and true replica prices: a unique, outstanding offer is likely a fake (and, of course, OEM must cost above replica every time). I notice local independent vendors charge above the MSRP found on the local BMW site (is your dealer greedy?).
The exclamation mark looks doubtful to me anyway.
