How does a store get ratings?

I need to get an '8' rating for a store but only get to 7. I've upgraded 3 times and have the right employee. Do I add more plants or something?

It's been a lonnnng time, but I sorta remember that improving the MALL rating improves the store ratings therein, and vice versa.

At the very worst, start a new profile and this time pay more attention to the boring pop-ups.

For your store to earn ratings, you can add decorations (flower pot), change the incorrect employee, build 2 shops of the same types together, and upgrade your store to the max. Doing this, you would probably earn 10 (maximum number of) stars.