Check the price against

www.bikepedia.com

and use the formula C Law suggests. ksl is a smoking location for tons of stuff! For the very reason that you suggest, there are tons of bikes available, it sounds like a buyer market. Play it tough, but respectful. Don't insult a bike owner, especially a MTBer close to the Wasatch Range. You might become part of the trail. Offer a price that is conservative, not insulting.