If you can get your hands on a red book, they give a little indication about how to grade. It's not a good source of valuation though. The little ribbon crooning the middle of the torch is a "high point" of that side. If this and the lines in the torch are clear and concise, that side values high. The outline if curls on the head and hat are high points and contribute to value on that side. Then you must look at overall background scuff marks and the pinwheel effect. All those factors determine value plus some.
Most coin dealers offer free valuations, so check that too. As stated earlier, Mercs aren't very valuable, with a medium of about 1.50 for them. The earlier ones are different of course, more valuable.
I had dozens of rolls and dozens of slabbed pieces among others that were stolen

it was worth upper 5 digits for all my coins. So glad to see your beautiful piece! The history is magnificent!!!!