I was meaning the sort of retailers that offer money back guarantee.
In the UK that is people like Staples, and including supermarkets like
Asda and Tesco. Many smaller local shops also offer that sort of
service.

eBay and local Sunday market are worth avoiding - generally speaking
that is... i bought a decent flash drive from a genuine enough trader
- always read feedback very carefully. You get what you pay for in all
honesty.