I first noticed this effect back In October 2010 ([webmasterworld.com ]), at that time others had already mentioned it. I've still not managed to resolve it.
Some of my observations:
1. I get 2-3 days per week of sales (if I'm lucky), the rest is almost dead.
2. Traffic Cap - traffic volume is almost identical each day (with a slight decline at weekends).
3. The 2-3 good sale days randomly change every few week, but they are always consecutive. For example, for the last few weeks it was fri-mon which was good. Before that mon-wed was good.
4. On good days, the traffic source countries have a higher percentage from the US and UK. On bad days, a high percentage of traffic comes from India.
5. about 80% of the search terms are hidden from analytic (this is obviously due to the new google rules).
1. My site contains both free, and non-free products.
2. The traffic share to the free pages has increased, and non-free pages decreased.
1. Google has perhaps weighted my site as having a high percentage of free content and sends a larger proportion of non-paying users my way.
2. The traffic cap is reached before much of the good, paying users are sent my way.
1. Split the website in two. One for free information, the other for products.
I'm concerned that if I split the site, I may damage it even more. Any thoughts?