I did a digitized analysis of the following item being bid on eBay at this moment:

China 1899 Red Revenue Tientsin Reg. to Shanghai Cover

Item number: 200012351879

My digitized analysis indicates problematic pa-kua chop on the Red Revenue. The digitized image of the pa-kua chop indicates uneven edges of the bars of the pa-kua and much darker ink that forms a sharp contrast with the degree of darkness of the pa-kua chop on other stamps. Genuine or not, you be the judge.