1 star for two reasons...
1. They give you a free shake only if you give 4 or 5 star review. I'm not looking for free anything. And you shouldn't have to bribe your customers to give you 4 or 5 Star reviews.
2. Evidently.... when you pay for shake you don't get a full one
Update!
So 16 months after I leave this review I received this private message from the business today...
"I find it really inappropriate to give a review like that with no proof about the yelp and a free drink. In your picture is nothing to see but if you write a review you get a free one, where does it show if you write a 4 or 5 star review? There is nothing to see on this picture, probably, because it's not the truth! If you put something like that out to me and there is nothing to see on this picture you're a straight out liar and I can't take you review serious! So where is the proof. I don't see anything wrong in getting a free drink, if you write a review. But somehow the 4 or 5 Star part is missing, or not even true!"
Readers, please note that in the picture of the sign second line from the bottom
"4 or 5 star review only"
As far as I'm concerned Mustang Sally still owes me 2 ounces of milkshake that I paid for.