Quality score in Adwords has been around now for probably two years. In most of our clients account we find that the things that we were doing two years ago (i.e., fine tuning keyword sets and testing ad copy) to improve conversion rates also drive good quality score. Recently, we've had a few B2B companies that have very focused niches with relatively low impressions on those niche keywords. We've seen a lot more quality scores of 4 and a few even lower than that. We spent some time working with our Google Adwords account rep to try to get a better understanding of what was going on. This is what we learned:
First, quality score is assigned based on closeness of keywords to search query, relevance (presence of keywords) in ads, relevance of landing page and historical click through rate. In terms of the landing page factor, Google indicated that landing pages are really just a yes/no issue and there isn't a range of score for landing page. That being said, our understanding is that the single most important factor is historical click through rate.
By default, the historical click through rate in an individual Adwords account takes 1000 to 2000 impressions over a 1 to 2 week period to be set and then allow your account to have a quality score for a certain keyword. Prior to this threshold, they use the overall average quality score for all advertisers who have tried to use that term. Quality score is assigned to exact match keywords so using extended match to try to accumulate more impressions will not help quality score.
The example stated involved the term "web hosting." When you initially bid on that keyword, Google will use the average web hosting quality score experienced by all others who have tried that keyword. That seems a little unfair if you believe that your "web hosting" is different or better than everyone before you. Google doesn't care... your initial quality score is the average. In the case of web hosting, you'll be able to get your 1000 to 2000 impressions very quickly so that you can accumulate your own quality score in your account.
Back to the B2B example. If some of these keywords will never have more than 1000 to 2000 impressions per month, then it is possible that the account will never establish its own quality score and it will work off the overall quality score average. We are left with two choices: 1) accept the system average quality score or 2) pause those keywords with really crummy scores. We've done a little of both with our current client.