My guess is, the graders had several choices of problems on this coin, and that's the one they went with. My guess is, this coin spent some time in the ground and was dug up. That rusty orange color is something I usually associate with environmental issues. After it was dug up, it was probably wiped or cleaned. The cleaning does not appear to be very harsh, from these pictures. Different angles might show something quite different.
I have decided not to bid on this coin but I am following the bidding closely since it ends tonight. Based on my research, I had estimated this would hammer (w/o BP) at between $7K and $8K. It is currently at $6750 with 63 bids. Pretty lively for a Details coin but it is a rarer die marriage. Let's see how close I got. I'll post the winning bid when the auction is over in about 45 minutes.
The 1798 Dollar, NGC AU-55, BB-82 Details-Improperly Cleaned hammered at $9750 with 73 bidders. Higher than I thought it would go for. Graysheet on this coin in AU-50 is $20K so its details grade knocked ~50% off the value. But the evening wasn't wasted. I got husband points for watching my wife's Hallmark movie with her and I won the three lots I was bidding on: 1871 IHC NGC Proof-64 RB CAC 1832 Half Dime, NGC MS-62 CAC, LM-4, R-4 1837 Reeded Edge Half Dollar, ICG AU-55, GR-17, R-1, MDS In case you're wondering, I always try to attribute die marriages and die states before I decide to bid on them. That helps to discriminate between weak strikes versus wear versus die wear versus poor grading.