This is the exact opposite of what we are experiencing at the moment. We have reasonable traffic (500k UVs / month, 9million PVs), but regularly miss out on campaigns that would fit our site perfectly. Infact, we usually see them on other websites (same industry, different space) and then call up the buying agency who have "already spent all the budget".
Frustrating! We have an advertising agent which is currently taking 35%. Between them and our backfill we still only monetize around 50% of our inventory each month.