Margot is revealed to be a high-priced escort midway through the film, but some of her behavior prior to the twist doesn't make as much sense as it would if she were actually Tyler's date: She's really put off by the fact that Tyler originally made dinner plans with another woman with a name that's not her own. That would certainly make sense if she's realizing that she's a "back-up" date, but Margot is an escort who is already using an alias.
Her first instinct might have been that Tyler gave a different alias for her when making the reservation. She could have just said, "Yep, that's me! I think they simply wanted to foreshadow Margot being an escort and Tyler being willing to let her die. In fact, I remember her barely reacting to it, which I found strange and later took as an early sign she was an escort. The only ones who seemed to care were the staff who realized this would affect their plans , and Tyler, who was embarrassed.
She's really annoyed by Tyler's insistence that she not smoke, and fights him on it. It makes sense for a date to resist his demand, especially if she's a regular smoker, but an escort must be asked all the time not to smoke while she's with a client. She could also just be annoyed at the way he's asking her not to smoke. He's kind of condescending, after all.
Consider also his reasons for ordering her not to smoke: "It'll ruin your palate. Most of the time, if a client of Margot's asks her not to smoke, they'll be requesting her to do them a courtesy; they're a non-smoker, they're trying to quit, they don't like the smell, whatever. Entirely reasonable motives for asking someone not to smoke and ones which she'd likely be perfectly willing to comply with.
Tyler, however, is getting on her case about her ability to fully taste the food; client or not, why should that matter to him? It's kind of an off-putting request for him to make.
