I say it's just as important to know grading if you want to go by price guide. Those high prices ate often about quality rather than simply one that still exists. A "mint" C-9/C-10 may not even run....nobody knows; never got ran 😉
The SOLD ebay search is a pretty good reference though. Toss aside obvious lowballs and highballs and that's that.
TCA's site has a guide for grading pre-war and one for Post-war; no pricing.
