Grading
Grading beer can and soda cans is a pretty established method. The Beer Can Collectors of America (BCCA) now has long established a universal grading system. This grading is numeric with grades between 1 (highest) and 5 (lowest). Grading also has plus and minus symbols for very fine grading. Grading cans with + or – can get a little subjective and takes many years of experience with a trained eye to accurately grade at this level. Other terms in the hobby are used and sometimes misused.
Here are a few examples:
Mint Condition – Think about this term. For a can to be in mint condition is needs to be in “perfect” condition. No flaws. Almost every can on the store shelf does not meet this criteria. This would be the best of the best and not a better example can exist. I personally don’t ever use this term.
Dumper – This term originates from collectors that started out only collecting cans they found outdoors or in weathered environments. Typically, a dumper can will be grade 2 or even lower then a 5. Dumpers are not graded. They are examples of a can that represent deferent meaning to different collectors but almost always not a high grade can. While there is value to these cans they are often traded or substantially less then higher grades. Again there are always exceptions based on rarity and demand.
Rolled – This is a real can it just was not completely assembled in the can companies assembly. It is usually a body blank or sheet that a few can specialist can roll in a form and seam then attach top and bottom lids. Any rolled can should be disclosed upon trading or selling for full disclosure. My experience is that a quality rolled can with rarity can fetch the close to the same value as a factory can due to the scarcity and most of the time higher grading.
My grading follows the BCCA’s guidelines and the grade examples on this site do not grade any beer can less then a grade 2. Again it takes a trained eye to see the grading in between the numeric order and gets a bit subjective.
Mint Tahoe Ok so to most this Tahoe can at first glance might be called “mint” however as I explained that’s near impossible and I still would not give this can that designation!
1+ Noch-Eins This can is like you would expect it to be the day it was on the shelf in the store. It is NOT mint but has no visible flaws that can subtract from the grading.
A1+ Eureka Very close to a new on a store shelf condition but a few indicators like the tiny spots on the spout and a few pin size spots. The little paint nicks would be consistent with new can from shipping and handling.
1/1+ Old German This can is very close to 1+ but observe the very slightest nicks and pin size spots and little tarnish to the lids
1 Old Dutch Has a scratch and 4 small paint chips 
1/1- White Horse Paint chips and nicks less then 1- but more then the grade 1 example.
1. V.R. Vat A very nice displayable indoor condition beer can however there are nicks, scratches, chips and a small indentation.
2 Imperial Obviously exposed to weather or humidity. A fine example, very legible and a great filler can but too many imperfections to reach a higher grade.
Value
Like collecting comic books, coins, baseball cards and other collectibles, the value of your collectible is greatly based on Condition, Rarity (supply), How many collectors want it (demand) and Exposure. Here are examples that can affect value:
Rare but not much demand – There are can know to be pretty rare but due to their graphic design, lack of information or just not anyone paying attention to it (a “Sleeper”) may not sell as high as a high demand can that is not as rare.
Supply – It seems like the hobby has phases of can availability. If multiple collector liquidate their collection at the same time or overlap that can create competition and may temporarily lower a cans value. Also there are more and more can dealers then before. This makes it easier to shop for the can your looking for and also creates competition.
A find – Say your holding a can in your collection that only 6 examples are known. It would be fair to say it is rare and most likely hold a higher value. Then a contractor finds a case of that rare cans at a construction site. Now once that supply gets out, typically the value drops. Now the rare can of your shelf decreases in value.
Classic design – Some beer cans are so graphical and is like artwork that that can falls into high demand even when there is quantity. These cans usually have a very predictable market value because there are many examples of what the can sells for.