When Greta and Frances get in the cab, the medallion number on the license plate doesn't match the one on the top of the cab, which they have to in NYC.
When Greta first stands outside the restaurant you can see a double-decker Dublin Bus quickly pass by. The movie was shot in Dublin, Ireland doubling as New York City.
Frances is seen receiving a call while riding in NYC Subway underground. You can only get a cell signal at the underground stations, but not while riding in the tunnel between (at least at the time the movie was made).
(SPOILERS) There's no reason why Maika Monroe's character should have to wait for months on the subway looking for Greta's bag to be left behind. When Greta had her fit at the restaurant, she would have been made to show ID, so the cops would have her address. It's clearly not hard to find; the detective found it later. It also strains credibility in a big way to imagine that of the 11 or so million people in New York, Maika Monroe would find exactly the back she was looking for.