Smart pricing is considered to be one of the main reasons why google adsense might be giving low cpc to ad clicks on a website. When I came to know about it, I tried to gather information on what it is and how exactly does it work. Does it work on per-site basis or effects an entire account. Most blog/forum posts were unsure and there were a mix of views on how it effects your earnings.
I recently found a very interesting and indepth explanation of how smart pricing policy of google adsense works or might work :
An author at the adsenseexperts forum says
First thing to understand is that traffic from different sources (publishers, websites, etc) converts for advertisers at different levels. (Conversion Rate or CVR).
So, to solve this problem, ad network "smart-price" which is a way of leveling out the amount an advertisers pays for clicks of varying quality.
Here is a simply example.
Advertiser is bidding $1.00 cpc on the term "buy widget".
Publisher A's traffic sells one widget for every 20 clicks (5% conversion rate). This means the advertiser is paying an average of $20 for every sale they get from publisher A.
Now, enter Publisher B. Publisher B's traffic coverts at a lower rate -- let's say that only 1 in 40 people actually buy a widget from advertiser. This would mean that the advertiser is paying $40 for a sale generated from publisher B. So, the ad network "smart prices" clicks from publisher B down by 50% to maintain the publishers eCPA of $20.
Why do they do this? Simple. If they didn't smart price traffic sources that covert at a rate less than average, the advertiser would lower their bid to compensate. In the above example, assuming that both publishers had the same volume, the advertiser would lower their bid to $.75 to maintain their eCPA at $20. This would cause publisher A's earning to decrease even through their traffic converts better and publisher A would then be better off going to another ad network that didn't have Publisher B in it, causing lower bids.
So, all traffic is "smart priced" to either the network average or the "best of network". This keeps upward price-pressure in the market and helps the network maintain high ppcs and high converting traffic sources.
Read more: http://www.adsenseexperts.com/advanced-adsense-publishers/smart-pricing-t11.html#ixzz2DlwIM5da
The author further says
You can still find ad networks that don't smart price -- they are the ones with the 2 cent PPCs because they fall into the above trap of continually losing high quality traffic sources which results in declining ppcs.
Adsense, on the other hand, most likely smart-prices by the most granular level with statistically significant data available. So, I imagine they have a base rate for an entire Adsense account, then by domain, then by individual ad placement or page / size. All this would be split by geographical regions as well. So, if you change your ad placements and you see increased clicks and earnings for a few days (or longer / shorter depending on volume) and then see click remain consistent but earnings drop (a PPC drop), you are most likely being smart priced. Try removing the likelihood of accidental or misleading clicks, leave it for a week or so (again, dependent upon volume) and you'll likely see PPC rise again. The trick here is to find the right balance. If you're curious how much traffic Adsense probably needs to make smart pricing decisions, consider that they probably have somewhere in the neighborhood of 75% conversion pixel coverage and then use an online statistical significance calculator to see how many clicks from each country you would need to send them for them to be 85% confident in a decision.
Read more: http://www.adsenseexperts.com/advanced-adsense-publishers/smart-pricing-t11.html#ixzz2DlwPICnX
What has been said, sounds quite logical and some conclusions that can be drawn are
1. A site must generate valid AND quality clicks. Just generating clicks is not enough because unless they turn into a profit for the advertiser, google will discount the price of those clicks.
2. Smart pricing is likely to have a account-wide effect. So if I am trying to earn a few additional bucks by creating low performing site or sites with just ads and no real content/purpose, then it will have an effect on the earnings of my main performing sites.
About some of the optimisation techniques
Many blogs talk about adsense optimisation techniques and one of them is to blend the color of your ads with the color of your website. Why ? So that visitors click accidentally ? thinking it is some useful resource ? But think it from the business perspective, such clicks will have a a low chance of generating any real profit for the advertiser of the ad. So this is an optimisation technique or spoiler ?
I am not very sure because I have not yet used adsense for a decade. And it appears that to generate a quality ad click, the ad must appear like an ad in the first place. So trying to "generate clicks" will actually bring in the smart pricing factor to balance the equation of earning.
In short publishers benefit only if advertisers benefit.