Pretty much what I thought. I judge the amount on the right, left and bottom of receiver and average it. In a nice gun, the covered areas inside are usually 100% but the triggerguard is usually mostly gone. Sometimes the buttplate was once cased but usually gone. That is best a side comment.
Of course, the reason it is important is that the Blue Book calls out different prices in 10% increments and sometimes those prices are $1000 or more apart. Lots of room for argument and advantage taking. I can see why most legitimate dealers try to stay with general comments. Some guns have 0% but otherwise in pristine condition while other guns with 0% are ragged yet they score the same %.
Let the buyer beware.
