I think I mentioned this in another thread about the Gigabyte Z790 UD MB I bought recently.
I was very concerned that the box it came in was not at least taped closed and the anti-static bag was only taped, not actually sealed. I thought there was a good chance it was not genuinely new.
When I went back to the (UK) specialist IT retailers and emailed them about this they were very understanding and said if I wanted to exchange it they were fine about that. But what they told me and have no reason to disbelieve them is that is how Gigabyte MBs are now presented.
In short we should not be blaming the retailers, although of course they could be adding to the problem by reselling returned items. We should be blaming the MB manufacturers for packaging these delicate pieces of electrical hardware with such a lack of care.
They are neither properly protected from moisture or shock damage and the boxes are not tamper proof which make it easier for unscrupulous retailers to pass off second hand equipment as new.
I blame this on badly considered 'green' environmental pressure to reduce retail packaging. Manufacturers happily do this. Why? Because it is cheaper just to use cardboard and not protect the MB with polystyrene, seal the MB in the anti-static bag and security tape the box and/or shrink wrap it.
But this is a particular case where that reduction in packaging should not apply. The PC building consumer is now left to take take part in a lottery where without any obvious damage to the box, like Shrodinger's cat, the condition of the MB can be considered perfect or broken or even replaced by a different cat with known issues, sorry, MB.

You won't know until you open it.
That is not how it should be.