Sorry, for me you need an "It depends" option as there is a wide spectrum here. I will readily share my knowledge with sellers who I have known for years and who have always done right by me (and fellow collectors). Then there are those sellers who routinely lowball on offers, whine and moan when you even ask on a better price, and/or just treat their 'customers' like crap. For those I have no problem NOT pointing out variations that could garner them more money. And I applied both cases at a show this weekend.
I probably use more of a "What goes around comes around" type of philosophy when dealing with this. Which is probably applicable to me in the way I deal with this as well.
