I would be surprised if the majority of people never experienced issues similar to Martin's.
Recently for an account, we had a Google Account Manager assist with optimising for higher conversions. The impact of having their help resulted in the cost per conversion doubling, and non-relative keywords being bidding on.
From my own experience, the quality of help you receive from Google is tied to the budget of your account. If you want some proper advice, I would suggest you seek help from an agency and not from Google.