I've played with 7 and it was perfectly fine. I'd have no problem playing with 8 either, but definitely not 9 because then someone doesn't get to draw a consumer card. You'll have to reshuffle the business deck once or twice and it's possible that you might run out of money, but you can always substitute something else in if you need to.
Yeah second this guy, the game play is still the same and still solid at 7 and 8. You will just find yourself shuffling the business discards a couple of times.