Revealing mistake: Ellen and the cab guy are having some stilted small chat during their drive across town. Just look outside the car window; yellow antique shop sign, blue sign, purple store, green one...They are not exactly generic and makes the fact that it is all takes of them driving down the same road back and forth obvious and hilarious. In the first wide shot you can even spot the fact that the road past the block they are driving through is clean, they didn't spray shaving cream down there. (00:17:30)
Revealing mistake: Even in the middle of the night just after a snowstorm and with plenty comments made about the freezing cold, the need for clothes heavier than the simple coat Ellen is wearing, etc., not the faintest hint of breath condensing can be ever seen throughout the movie. Exception are very rare; once in front of the hotel when Ellie ships the truckload of auction items.