How to pick avocadoes with small seeds?
You must remember that studies have shown that a normal avocado will have between 60% to 70% flesh. According to this Mental Masala blog post


  The edible percentage is consistent across the span of weights, centered around 70%*, meaning that the amount of flesh you get from a Hass avocado is relatively independent of the total weight.  The 70% result is consistent with UC Riverside's Avocado Information site, which states that the seed, skin, and flesh percentages for Hass avocados are approximately 16%, 12% and 72%, respectively. 


So, it presents that across a test group of 19 avocados, there exists a linear growth pattern. Therefore, you could say that you can go to a grocery store and pick out any random avocado and it will very likely have a 15:15:70 ratio of seed:skin:flesh. Now, there could be the odd outlier with 1:1:99 or something, but that would be rare.