The biggest problem is most fruit is picked before it's ripe. It keeps longer on the ship and gets ripened with gas when it is unloaded at the destination. We pay lots of money to get fooled here in north europe.
Avocados do not ripen on the tree. They need to be pulled off in order to ripen properly. You need to pick them at the right time so they have the right amount of oil content.
Of course, there's also the quality - or not - of the soil.