Since so many new buyers seem to think they can "steal" a property, and at least locally, they can NOT. I simply ask them this question, "Since this seems to be the best home for you that we have found, and it is in your price range, is it going to bother you if you lose this property to someone else that may be making a more reasonable offer, based on current market values?" Mr. buyer, I have had several buyers lose a couple of properties by lowballing their offers before they finally realized that I am telling them the truth... that scenario really happens regularly.
They still get to make the decision, but it's your job to tell them the possible consequences of irrational decisions. One recent educated buyer asked me why shouldn't he offer 10k less than asking price and see what happens. This was a VERY popular neighborhood, and all nice homes priced well sell quickly. I simply asked him that if he were the seller, and his neighbors all around had been selling for 200k, would you settle for 190k if you had the data to prove you are very likely to get 200k? His response was that the logic does make sense, and not willing to risk losing the home he really wanted for a "crap shoot".