Will photographs of graded coins defeat counterfeiters?

And, a lot of times a coin has neither a low mintage (and still exist in numbers exceeding tens of thousands of examples) or a high grade - and is still very expensive, even in low grades !

Which brings us to your primary question -

In the end it usually boils down to one simple word - popularity. If a coin is popular regardless of its mintage, regardless of its grade, regardless how many still exist, it's usually going to be expensive.

But if a coin is not popular, it can have very low mintage (even under 100), it can be a high grade, and it's still inexpensive, cheap even.

 

And Blake, on the subject of the TPGs certifying counterfeits as genuine coins - it happens far less often with US coins than it does with world coins. Take Netherlands gold ducats for example. Between the top 4 TPGs, ANACS, ICG, NGC, PCGS they have certified thousands of counterfeit Netherlands gold ducats as being genuine. And there are plenty coins from plenty of other countries that are counterfeits but have been certified as being genuine by the TPGs.