X-T3 mark on sensor

I am thinking about buying a used x-t3 from mpb.com, the description says it’s in good condition but that “The sensor has an irremovable mark, but this doesn't affect the final image produced.” I’ve heard mpb is trustworthy, but it seems hard to believe that a mark on the sensor wouldn’t affect the image taken? Would love some input before I pass it up or buy it. Thanks!