starrymarkb
Established Member
Royal Mail do, and add an admin fee on top.
I recently experienced this, however the sender warned me, and I didn't bother claiming it as it was a brochure from an estate agent.
Estate agent told me not to bother collecting and paying as they realised they hadn't paid postage straight away, and they sent me a replacement brochure correctly
I've recently had one where the franker had managed to print postage of 0p - though Royal Mail recovered it from the sender (the letter was stamped "shortfall paid by sender, treat as first class")
Amusingly it was a bill from the landlord!