I am curious about how you can tell the difference and how much the banker’s mark affects the value of the piece.
Okay. The mark at 2k is probably a planchet flaw. The one at the 6k is probably a bank's mark. Is that correct? https://agoraauctions.com/pegasi/listing/viewdetail/13814
It's in the link which is to a "safe" auction site. They won't let me download the photos. I would if I could.
If you need to take a picture in the future where the website does not allow downloading, screenshots and a snipping tool are two good options. If you use Windows, these links should help explain each process (it is a bit different for Apple) https://www2.owens.edu/faq/entry/67/ https://support.microsoft.com/en-us/help/13776/windows-10-use-snipping-tool-to-capture-screenshots
In this case I think both spots are the result of the process of making the coin. The 6 o clock spot looks like a spot where the edge split from spreading during striking.
Both are "natural" flaws/artifacts of the striking process which detract little and often enhance the appeal of ancient coins in my opinion.
It would be quite unusual for a banker's mark to show up on a Commodus denarius. For reasons I do not understand, banker's marks are far more common on Republican and early (Augustus) denarii. I agree that the coin in question has an edge flaw, probably as a result of a small planchet lamination. Here is a Faustina denarius with a more dramatic example of this:
I don't have any facts, but I have a theory as to why banker's marks decreased in the later Empire. Perhaps it was for the same reason that there are almost never any marks on modern US coins, even pre-1965 silver. The coins, even silver coins, were given higher fiat value than precious metal value. There was no reason to test a coin's metal because it was relatively insignificant. That would be why many of the later Roman coins were silver plated yet circulated without test marks.
That is a good theory. The prevalence of Chinese chopmarks on Spanish silver dollars (and US Trade Dollars, etc.) would fit in with this theory - they circulated in China based solely on their weight. There was no "fiat" aspect to these coins, just their bullion value.