For the same campaign, the keyword is easy to get a "great" mark in a brand new account than in a long used account.
Yes, Google tends to give a more positive quality score rating initially. However, check back in a day or two and you will likely see your score has been adjusted. If your quality score remains high for a longer period of time than what you are used to then your CTR and keyword history are the variables that are pulling your quality score down (considering all other factors equal). Here are the factors that go into Google's quality score. - Keyword relevance - Ad copy relevance - Landing page relevance - Click through rate (CTR) - Keyword performance history - Other relevance terms Google will not share