When did he buy the bat and how much has he used it before it cracked? Was it honestly just through very general use and had it been knocked in etc? Maybe send some pics to assess.
If it's new/hardly used and was just through general play, then to not offer any type of repair or replacement is poor imo.
What I would say is ping and pick up, are to some extent, open to interpretation. What one person will feel is good, another won't. Pick up more than ping, but even then if someone is comparing a fully played in bat to a brand new one, it won't feel as good.
If it was heavier than advertised/requested, then I'd have sent it back initially. However, if a bat I sold cracked badly shortly after use and it wasn't obviously mistreated, I'd offer a repair at least if not a full replacement.
Either way, I'd be fighting them on it personally -
https://millichampandhall.co.uk/pages/warranty?gad_source=1&gad_campaignid=21153634452&gclid=CjwKCAjwi-DBBhA5EiwAXOHsGQaol--ct2FWFNF4sUZ7j4w-lSxYqxRkgteXr15VF5Dncdt_9fv0QBoC-M4QAvD_BwE