CPO iPhone XS Max Screen Issues?

I just received this phone in the mail today. Immediately after powering it on, I noticed something was up with the screen. There’s a blue mark on the top right corner of the display that looks like a bruise. Blacks look blue and there’s a faint purple hue when I drag items on the screen. In addition to that, the bottom bezel of the display is remarkably thicker than the other three bezels. What is going on here? Was the screen replaced by an LCD? When I hold this phone next to an iPhone XR with both displays set to 100% brightness, the XR’s supposedly inferior screen looks significantly better. The colours on the XR are more accurate, and the blacks are even darker!
Nowhere on the order page indicates the possibility of this occurring. In fact, it says “OLED”. Have I been duped? I understand that the phone was previously used… but I feel like a fool because I read thoroughly through everything before proceeding to the order page. I was led to believe that the phone was returned in working order, inspected for faults, passed and thus deemed fit for sale. What’s going on here??
I’m fine with a few scratches or nicks here or there as that’s what you’d expect, but I don’t feel comfortable risking the longevity of an aftermarket LCD screen with a source that I can’t verify. I’ve heard too many horror stories of such replacements going wrong, and I certainly don’t want my phone to be borked outside my 30 day window, and have to pay again to repair it. What gives?