So what are the phrases that immediately make you concern once you hear them from a rep, network or traffic source?
Two for me are, with all their variations:
"To be honest..."
"I'm being transparent.."
As soon as I hear either one, and really they are variations on each other, I immediately question the honestly of the person saying it. It implies they haven't been completely honest and are trying to convince you of their honesty now.
"We really appreciate your traffic, but..."
"We are almost losing money on this, can't go any higher..."
"I don't normally do this..."
"Just between us..."
I could go on and on
)
In most cases I don't need a phrase... 
If an AM contacts me without me knowing the reason beforehand then usually it is not the best news.
My "favorite" so far was: There is one more thing....