It's good to know who your competition is going into a bid. If an EC is known for doing work for a certain GC, there's a chance that guy gets bid day feedback. That GC is just trying to get his guy the job, Nothing you can do about that except proceed with skepticism and remember this when they ask you to bid another. It's when the GC is giving several EC's feedback that is crappy because it spreads everywhere because face it, just about everyone has someone that gives feedback.
I worked for a company once, before there were even fax machines to fax your bids. You had to hand deliver your scope letters the day before bid and then call in your bids. The last minutes of "gamesmanship" was nuts. We had every estimator making last second calls to all bidding GC's and distributors, lighting reps, collecting feedback swirling around. These calls you heard a lot of "how do I look" "did you use my number" "will $$ get me the job" "don't give this number to anyone else"....It was so bad, my boss would put out different numbers to every GC. If that number floated back to us, we would know who shopped our number.........it was crazy