Can you not read plain English? Simplifying what I said:

Yes I can read plain English and what I am saying is that your statement of
the law in this case is wrong.

He has a claim for the REPLACEMENT cost of his shirt in the
condition that it was.

Indeed and that means effectively the second-hand value that is likely to be
very small.

You cannot demand that he spends hours of time and many pounds
of money searching second-hand shops for a suitable replacement,
but you can refuse to pay for the "worn" aspect of the shirt.

I demanded nothing! I simply stated that if YOU wanted to establish what the
open market value of second-hand shirts was then a charity shop would give
you a reasonable idea of how much they were worth. At no time did I suggest
that the person concerned should take that they should seek a replacement
there. It seems to me that it is you that cannot comprehend plain English.
If it went to court and the claimant won he would would not get more than
the open market value.

A fiver is insulting.

Far from it. It is a realistic statement of the likely worth of the garment
on the open market.