He is behaving honestly with the restaurants but not with his followers. Unless he is actually posting things like:
"Hey, I've never been to Moe's Tavern but they said I could have a free burger if I posted this picture, so here it is. Go check it out! You should totally spend money there. Moe's is awesome!! (at least, they were awesome enough to offer me a burger to type this!!11!!!)"
I wish this craze go wider and wider, so people finally stop believing what they are told from billboards, TV screens and social media apps.
I don't think that agency selling places on bus stops has actually tries any of the promoted products.
So ethical or not, it's illegal to not disclose.
Which is why I hate ads, and most online reviews.
Forget about all the other morally grey things about this, this is blatant copyright infringement. There truly is no such thing as a free lunch, the content is where 100% of the work and money is, and its completely stolen.
I re-read his article to see if he took steps to work around this. My god, he even seems proud that he directly scrapes from other people's instagram. I would go as far as to report this guy.
If he were copying and pasting the images, that's one thing, but what he's doing has no losers - it amplifies the original user and falls within acceptable instagram practices.
That doesn't mean that I don't feel slimy about the whole thing.