Saw this Uncirculated "raw" Seated half dollar at a great price in Baltimore this weekend. Almost pulled the trigger but remembered: "There is no Santa Claus in Numismatics." Then I saw this... One thing that has helped me in the past is to treat every coin I look at as a problem coin and look very carefully for the problem. Then, problem coin (cleaned, damaged, rim file, etc.) or not , I can make an informed purchase.
Nice post. I had a half dime with 3 of these exact same areas on it, hidden beneath toning spots. Someone tried to scratch away the spots. UGH!
I have a Morgan where someone outlined the eagles left wing with a knife or something. Hard to notice unless it's right up in your face or you're looking at a pic of the reverse.
That's often a hard alteration to detect. I've seen lots of coins with outlined devices. As long as the cut is right next to the relief and dark it often is overlooked.
It definitely helps to approach coins the way insider does. I bought this seated dollar years ago noticing it had some issues but I missed the initials carved on the obverse. I still like the coin but it forced me to scrutinize more.
I don't think the PCGS graders missed this. I choose to think they did not believe it would lower this low grade coin's value. Thus they ignored it.