How Quality Score Discriminates Big and Small Accounts

Quality Score shown into your adwords account includes, many relevancy factors including average quality score of all the keywords in your account. Larger the size of your account, more stable the score becomes. This is a sort of inertia developed within your account around which all keyword level Quality Score tend to align. Larger your account size, more stable this number becomes, lesser the deviation of Qualty Score at Keyword level. But, this means larger account gets the benefit of this average and wins in situations where Quality Score may act as barrier for smaller accounts. There are situations where some keywords which are of fringe importance for advertiser gains Quality Score because of this average, and wins over ads with perhaps more relevance.

So, larger the size of account, higher the exposure, lower the cost per click for you!
For small accounts Keyword level relevance is more important and because of lesser number of keywords can be afforded to go beyond the central theme, you are more likely to be punished whenever, you try to go a bit further. Why so? It is because every individual KW level Quality Score cause greater impact on account level Quality Score average, in a smaller account compared to what it does in a larger account. It is the reason why smaller advertisers find frequent account problems of keyword getting marked Poor compared to what Big advertisers faces.