Here is a little longer list:
Does the style
match the expectations for the type
? (Strange style
may mean pressed or struck with modern dies.)
Does the metal match expectations for the type
? (Many replicas are made in a different metal than the genuine original.)
Does the fabric
match expectations for the type
(thick, thin, squared, oval, round, etc.)?
Does this coin have the expected edge for the type
(ragged, with or without sprues, beveled, straight, etc.)?
Does the strike match expectations for the type
(weak, strong, even, uneven, centered, off center)? (Perfect on a type
that is almost never perfect needs close examination.)
Do the flow lines match expectations for the type
with similar die wear? (Particularly for some Roman
silver, the more apparent die wear, the stronger the flow lines should be.)
Does it have edge cracks and splits within normal expectations for the type
? (Too few for the type
may indicate casting. Too many for the type
may be a sign of machine pressing.)
Does the weight
fall within expectations for the type
? (Some types
are never light. Some often are, but underweight is still
a reason for a closer look.)
Does it have casting bubbles?
Does it have casting pearls from bubbles in a mold created by casting?
Does it have a ghost line indicating the edge of an original coin used to make the mold?
Does it have missing legend
or parts of the type
and indications that it was cost from a mold made with a coin with those parts off flan
Does it have waves in the fields (from uneven cooling after casting)?
Are the fields unusually flat? (May indicate machine pressing)
Does it have filing on the edge?
Does it have a casting or electrotype
seam on the edge?
Are the edge cracks and splits real?
Does it have tooling?
Does it have a natural patina
or an artificial patina
? (A genuine coin may have an "enhanced" patina
, but a fake coin will never have a natural patina
Does it match any fake in the fake coin reports
Is it for listed on eBay
by a member of the Notorious Fake Seller
Is it for sale on eBay
and the seller says no returns
or has private listings?
Is it for sale on eBay
and it is a very rare type
or emperor, misattributed as a common coin?
The challenge of authentication
is not just knowing what to look for, but also knowing what is normal for the particular type
says they do not guarantee authenticity, what they mean is they aren't going to give you any money
if they are wrong. How could they? You pay them $45 and they are going to guarantee your $5000 coin or even your $500 coin is genuine? Really they don't guarantee grading either. NGC
authenticates coins and they have expertise. The guarantee limitation is not even worth mentioning. NGC
is an unbiased highly expert opinion worthy of considerable respect. They can be wrong but they are more likely to be right than you are (and you means almost everyone).