I follow quite a few dance schools on facebook / insta from the days of my DD & DSD dancing (and have attended a couple). There is one dance school that very often uses pictures from online in there posts / ads. They don't state 'not our dancer', so unless you know / follow the school you are likely to presume it was one of their pupils.
On thinking about it, it could apply to any business really, pizza shop using an online pizza image, valeter using a brand new car etc.
If you knew a business did this, would it put you off using them? and should they have to state 'not our image'.
YABU - it doesn't matter its just a photo / ad
YANBU - of course it matters, its misleading and makes you think that is what you are buying