I think many current supermarket staff these days are way over-qualified!
In recent years I spent 14 months working in an M&S store, having initially been taken on as seasonal Christmas staff in a huge store, and then offered a p/t post in a new store opening in the following Spring.
I have a degree and have run my own businesses, as well as working for government departments, an university and the NHS in a long and diverse working life.
Amongst my colleagues on the tills were a former tax inspector (made redundant), a former bank manager (made redundant) and several former business owners, who (like me) went bust.
We made up the majority of the staff, and from my experience, we were not an unusual store!