I saw a 69 (perfed 12c black washington, oval ornaments in the corners) on
ebay recently in a similarly trimmed condition being offered as a 17 (imperf 12c black washington, round rosettes in the corners). It's was as glaringly obvious as this is not a 13. The seller was suitably embarrassed when I informed him, as he had bought the stamp assuming it was a 17. The moral being, even if the original trimmers intent wasn't to deceive, deception can still happen.