How to tell a proof from a business strike on 18th century material?

[CoinPictures-migration]

A bit of background: About a month back I bought an 1806 1d that NGC had graded as PF64 BN. The dealer I purchased it from was quite insistant that it is not a proof, but rather a business strike with PL surfaces. They've dealt with these coins far more than I have, so I'm not about to doubt their assertion. I have sent the coin into NGC for either confirmation or correction; will probably be a few weeks before I receive the results.

 

Fast forward to today. I receive another coin that may or may not be a proof. It is a 1770 1/2d that NGC has graded as MS64 BN PL. It has the most prooflike liquid mirror surfaces I've ever seen on a coin of that age.

 

The $64,000 question: How do you tell a proof from a business strike? What are the telltale signs? Do the "chiseled" characteristics of the lettering mean anything?

 

Some pictures below. First 2 are from the dealer; the remainder are mine. Apologies for the crappy photography; I absolutely cannot capture the mirror surfaces.