First of all, I have to give you applause for the honorable position you have taken and your dedication to upholding it. Not all journalists have those kind of standards (yeah, I know, call me Captain Obvious).
With regard to a continuum of negative - positive in this context, I think there is a great middle that is simply "true." Too far to either end becomes troublesome, but the great middle ground is simply there, like it or not. In the case you cite, it sounds like the sentence you point out is well within the safe middle ground. It is the rest of the ad that gives the statement context that could potentially warrant critical scrutiny.
By the way, you have now established your credentials as far as fairness and determination to follow your rule. You are in the driver's seat. If you say "No" in the future, then "No" it is. Well done.