My 2 cents. It is the "Golden Rule" as was stated above. Treat others as you wish to be treated. Also maybe before you hit the post button, double check what you wrote to try to make sure it doesn't sound "dickish". Remember, its hard to inflect tone into something that is written. Its hard for people to get sarcasm etc.

I personally have no issues with someone pointing out in a FS thread / ad that the price may be out of line. I think that it does a service especially for the people that may not be totally up on current prices. Maybe a noob that is looking at the ad perhaps to purchase. If you are selling, you can ask anything you want, and the market will eventually dictate if its a good price. Again, my 2 cents. Also there are ways to point out a high price without being a dick.