A good way is to find a second hand/antiquarian book seller (check the yellow pages) and take it in and ask them...it's often based on the condition, which can include the health of the binding, whether the hard cover is "bruised" (ie bumped) around the edges, the colour and condition of the paper & the colour plates (ie clean or age speckles, browned, tears etc), as well as more specialised info such as the number of copies printed in that edition, etc. It's going to be worth a lot more than $1, at any rate!