Diner Dash

To get this achievement, you will need to make two VIP/restaurant reviewer happy during one sitting of the game (I think your star level resets to 3 if you quit and continue the game).
The VIP has no colour and is always a single customer. She wears a funny looking hat and glasses (pretty easy to pick out of the normal patrons). Serve her quickly and get her out of the door. The sooner you do that, the quicker you get the star. A happy VIP means you earn a star, frustrated VIPs probably removes a star from your status.
I'm not sure if VIPs are random, but the first one is 1-7 and the next one is at 2-6.
You will most likely need to do this in one sitting since it seems like when you quit and continue a game, you are set back to three stars.
Upset customers don't take stars away (I'll double check later). They only take 500 points from you so you may not achieve expert status. So take your time and keep those VIPs satisfied.

To clarify on the above, the critic arrives on the 6th level of each restaurant. Guests leaving only lowers your score but you do need to pass each level but only the goal score though expert scores tie in with other achievements. You MUST do it in one sitting and if you have completed levels and go back you have to follow the storyline, i.e you can't just do 1-6 and 2-6 unfortunately.

it is a pain if you missed this first time like I did but at least getting this achievement doesn't leave you with a gamer score with a 3 or 8 on the end.