Most little bottles I've seen had a little paper tab that indicates the bottle has been opened.
But I always carry a bar of travel soap - I don't much like shower gel - and my own preferred shampoo and conditioner in my toilet kit. If the place I'm staying has stuff I like, I'll use theirs, otherwise I'm covered.
Btw, on threads like this, I can see nothing more useless than calling "fake" on the OP that's the basis of the discussion and sharing of our various views. You don't know that, and if you feel like that, why bother contributing at all? And how does it add anything to a discussion of whether bulk toiletries are a good or bad thing? And in the end, in terms of subsequent contributions of other's views, how does it matter whether it's true or not?