I recently bought this buffalo nickel which the seller claims was AU, it was going for $10 so I decided it was a pretty good deal if it really was in AU. The only problem was I couldn't find any photograding site that had the 1913 type 1 buffalo nickel.
http://www.pcgs.com/photograde/#/Buffalo/Grades Here's the link from PCGS. I would go VF35 if it wasn't for the rims, that's a lot of detail for the rims to be worn down into the tail and liberty.
It looks like there's hair details on the bison's head, so maybe that's why he thought AU. The horn is full too as far as I can tell
MKent linked PCGS's photograde page, also try their iOS/Android application. It's free and the images are great for on-the-go.
OP: There are factors such as worn dies, or weak strikes, or even a combination of both that will make a coin look more worn then it really is. Blah, blah, blah.... IMO, it's an academic discussion only. If a seller wants AU money for a coin I want a coin that looks AU and not a list of techinal reasons why it looks VF20, which is what it looks like to me using Photograde or VF30 using a rubber-ruler. Buy the coin not the excuses.
Acccording to photograde you would be lucky to get VF20. PCGS photograde would probably give it a VF 20-25
If you enjoy the coin I wouldn't be overly concerned with a few dollars here or there. You did fine for 10 dollars and will get to enjoy it longer than you would a movie ticket.
