This could be tagged access=customers but https://wiki.openstreetmap.org/wiki/Tag:amenity%3Dtoilets says that the tag is intended for toilets that are public but require a purchase. It also says the tag amenity=toilets should not be used for toilets that are not public. So properly the POI should be removed, rather than retagged -- unless somebody knows of a tag other than amenity=toilets to describe it.