Tonight, and it's been a long night since I'm posting this at 5:30AM I learned more interesting stuff from Chad's comment than I'd learned all day.
I have to concur with his assertion that you trust the people who show you where all the bodies are buried. When I first started out working with customers going negative on the competitors product was the instinctual thing.
It doesn't get you very far but it keeps the sales person happy.
One day sick of banging my head against the wall I set out to step on every land mine possible at every opportunity. It could have been a career limiting move were it not for the fact the customer, who the account team clearly didn't stand a chance with, leaned back in his chair pointed to the screen and said "This I can live with. Get me a quote on that." He then looked at me and said "I like you. You obviously have no internal filter which means anyone could tell if you were lying."
Don't think for a second I didn't have an annoyed sales bod looming over me the moment the customer left the room, had things gone the way they were already going I probably would have taken it in the neck, but the situation reversed and they closed the deal.
I most certainly don't advise anyone to be as unvarnished (Again, I've been told by some of the big brains I run a "Tact Deficit"), as I can be but you should advise people the way you would want to be advised.