Other mistake: When Quaid goes through the x-ray machine the first time, the person behind the man with the dog isn't shown to be carrying anything (there's no purple object shown). But then later the purple object is seen.
Continuity mistake: In the apartment, Lori grabs a knife, and after the first slice, switches the knife to her right hand. After the second slice, the knife can be seen midair as she tosses it from left to right again.
Plot hole: It's revealed by Cohagen that he had everything set up for Quaid to get to Quato including convincing Quaid that Benny was an ally but there's no way Cohagen could have known that Quaid would have chosen the other taxi driver instead of Benny. So if Quaid had picked someone else or even decided to walk to where he was going Cohagen wouldn't have got anywhere in drawing Cuato out.
Plot hole: At first the movie implies that Dr. Lull did erase his memory of Rekall, because when Harry told him he went to Rekall he had no idea that he had been there. But later in the movie he remembers that he chose "demure and sleazy" when Edgemar is talking to him.