the NADA guide John linked above is about the only generally accepted one - most appraisers and insurance folk will refer to it .... but have your salt shaker handy, few people selling a truck pay any attention to a guide, they ask what they think they "need" to get out of it, either because they put that much into it or there's bills to be paid and it's their only asset or bcause they think they have a rare jewel

Bill