Selfridges / Cartier would not accept our return and this appears common practice.
BEWARE.

I have been after a Cartier “Love” ring for the last 25 years!
My wife kindly surprised me with this for a large wedding anniversary at the end of August.
Cartier didn’t have my size in stock and directed her towards their concession at Selfridges.
She ordered from the Selfridge’s website and paid by PayPal, instead of our American Express as she didn’t want me to see the statement and ruin the surprise.

We opened the package from Selfridge’s together and I tried on the ring. Unfortunately, the ring was too small for me and after less than a minute of trying to get it on my finger, we carefully put it back into the packaging and use the Selfridge’s website to have DHL collect the return.

A week later we still hadn’t heard from Selfridges, so we chased them.
They came back with a rather shocking response…

They said that after rigourous examination the ring was damaged and therefore they would not issue a refund.
This is simply not true. We had the ring out for less than one minute and we did not notice any imperfections with the ring. We certainly did not damage it.
I know it is hard to trust people, but I am a regulated individual and I swear on both of my parents lives (aged 84 and 87!) that we did not mark or scratch that ring in anyway whatsoever.

£2000 is an awful lot of money to us and what was meant to be a surprise gift has ended up badly backfiring.

A simple Google search shocked as further. It showed that this was very common at Selfridges, especially from their Cartier department, which is incredibly alarming for a store such as Selfridges.

Moreover it is a common issue, as found on a simple internet search.