Decreasing yield - causes ...

I've been thinking of late - what is causing the decrease in yield across some areas of digital media.

Namely sales and the agency world.

Is it an increase in supply that is to blame (commonly stated), or is a decrease in the skill level of those working in the industry the real issue?

I don't know ... but I do think that both are probably playing a role. People tend to move on price when they aren't confident in their offering or don't know how to position it adequately.