Sadly a common occurance at Royal Mail sorting offices and mail centres
It is believed that the new management haven’t invested in new hand stamp equipment for mail that is rejected by the Ink-jet printers (usually the older, old rate stamps and out-of-position stamps).
Roughly 3 out every 5 pieces mail from/within the UK has the dreaded Ball-Point Pen or Permanent Marker.
I gradually got to known which are the worst offending and best mail centres.
If I know the postcrosser I am sending my card to is appreciative of stamps, I sometimes route my postcards through one of the three RM special handstamp centres, sometimes adds 2-3 weeks on the card.
Alternatively, I sometimes ask the Post office to cancel the stamps with the counter date stamp, but some post office Clerk’s don’t like doing that,