Bought this One Plus 6 in order to install Linux on it to experiment and test the state of linux on smartphones in 2024.
The product photos therefore show it running PostMarket OS, not OxygenOS-Android.
About my experience with BackMarket:
Sometimes difficult to know where the package is, and the box is much too big compared to the contents.
However, in my case the phone was well secured in the box and therefore protected from shocks, contrary to what you might hear from other reviews.
Concerning the condition of the phone:
The phone is in excellent condition, I have the impression that it is as good as new. It came with a charger, which is probably not the original one, but it works.
Before installing Linux on it I obviously quickly configured Android (Oxygen OS in the case of the One Plus) to install BackMarket and do the tests: everything worked.
I didn't test the battery under Android because I was impatient to start my experiment, but under Linux, without using the laptop (in standby) the battery lasts much longer than 2 to 3 days.
Regarding my experience with Linux :
I was able to install linux (postmarket OS) on it without any worries via the web flasher after unlocking the BootLoader, as the One Plus 6 is one of the best supported laptops. I was worried that I might have hardware problems if the parts had been changed during the refurbishment, but that doesn't seem to be the case.
The camera doesn't work under Linux, I should point out that it worked perfectly under Android and that it was totally expected that it wouldn't work under Linux. I'm sure there's a way of making it work, but I haven't had time to do any more tests yet.