Even to disrupt a scammer???!
There is a difference between calling someone out for blatant scamming, and telling someone There was a sale last week at an obscure retailer in your city and you paid $10 less than someone's asking price.(just as an example)
If someone is trying to say that they can't find 5970's for less than $550, and is saying he is the cheapest by selling his for $500. (scamming) I think it should be ok to correct their statement and point out that there are some lower. But if someone is selling 5970's for $400 (legitimate), It shouldn't be ok for someone to come along and say you saw some go for $300 on Ebay last week.
In the last year, I've sold 5970's for $700-$800 each. That doesn't mean they are all worth that much, I just found the right place to sell them, where someone was willing to pay my marked up prices.