Whole PREMISE is farfetched (SPOILER)
These are relatively young people who grew up with internet service etc.
WHY would they think that just because a stranger sent them, or posted, a PICTURE...that the picture of the stranger is REAL ? ? ?
So the "shocker" that this ideal stranger isn't who she says she is would seemingly have occurred to them much, much earlier on...like, when they first got pictures of this classically modelesque-looking girl out of nowhere.
It makes the main guy and his friends seem pretty thick-skulled throughout the whole movie, that this possibility never sinks in for them.
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