I can't help feeling that the shop should have checked the number of pearls when they came back from the restringing place. Your receipt was for 81 pearls but they only gave you 79 back so the shop is at fault as well!
(No consolation, I know, but it doesn't reflect well on the shop)
Good Morning Saturday 20th April 2024
Estranged Son and Future Granddaughter
To think that London, or anywhere else for that matter, does not belong to any one demographic