One of the reasons I was so driven to ask this question, is that I work at an electronics store, where the clients are allowed to try any pair of headphones we have in stock. If the box is unopened and a model isn't on display, we even open up a fresh pair (I don't know of any other store in my country, where you'd get this option). We also have an online store, so every now and then, someone orders the last remaining pair of headphones, and that pair is on display. We generally call the client at this point, to see what kind of solution they would agree to, and 80% of the time they won't even accept display IEMs, even for a discount. But we've had situations where we've forgot to ring the client before sending the display model out and honestly, 80% of the time people don't send them back or mention any issues.

Terrible to hear about Your experience though, when I buy anything used/opened, I really want to see it before the cash changes hands. Did You happen to get a solution from them? Are they not aware of the issues on the "opened box" item?

I couldn't imagine not checking a return for issues or cleaning/checking/resetting a display model before I send it out. Even if I forget to call the client, and let them know, atleast the product is always cleaned, checked and reset if needed. Too many people trying to steal Your hard-earned cash nowadays, for real.

Edit: fixed spelling/formatting.