Mexican Restaurants and Guacamole

At The Jones, our primary purveyor is Food Services of America who distribute to a large portion of the restaurants in the area. We buy most of our meat, produce, dry goods and other basic restaurant necessities from them. They charge us 12 dollars for a box of 10-13 avocados so they cost a little more than a dollar each. Restaurants that do higher a higher volume of business tend to get slightly better rates on things they go through cases and cases of every week i.e. Mexican restaurants and avocados. So maybe I'm way off base here but I'm assuming that in general they get better rates than we do on them. So one would think that a 4 dollar side of guac should yield you a serving size of 2/3rds of a cup or so especially since the bastards always bulk it out with a bunch of sour cream, and yet there has not been a single time in my life when I have ordered a side of guacamole at a Mexican restaurant and not been disappointed by the portion size. I bet the more corporate leaning chains like Azteca and such don't even make their's in house so its even cheaper. WTF Mexican restaurants? I find it really hard to believe that you are all costing your guac at an honest 25%.