One of the steps (not sure which one) took me forever to pass. I finally began taking it at the allowed interval, changing only one answer each time. If you have 24 right, and you change Q1 and then you have 23, you know that Q1 is right. Do this over and over again until you find the errant one. If I recall, the one that had me stumped had "trick" wording with the main part of the question not where my error was.
For what it's worth, very few extra shops opened up after getting to Level 9. The levels mostly just put you ahead of shoppers at a lower level.
Now scheduling travel shops for the day after Christmas through mid-January.