I recently tested all of my D20's for fairness, this was the worst offender after 100 rolls

I tested 17 D20's today and the spread was definitely interesting

I had 3 that had averages over 11 and only 2 under 10

3 of them had the most common roll being a 1 and 1 had 2.

Funnily enough the 1 with 2 as the most common result had an average result of 10.73. So it was still favorable to the dice roller as it beat 10.5.