I'm personally seeing enough red flags to pass on that one just based on the packaging. If I can't see the device being offered in the listing photos, I move on. That means if it's "sealed, new in box," I'm immediately skeptical. You can buy 100 official looking S23 tamper seals on Alli Express for just a few bucks. At the very least, require being able to open the box and examine the actual phone prior to completing the transaction. If the seller hesitates, hard pass. Breaking the seal when it's already being sold at a steep discount isn't going to change the value and refusal screams scam.
The box itself looks fishy to me as well. Someone with more knowledge than me would be better to confirm, but that particular style of box shouldn't have a seam/line running down the sides of it when compared to other boxes I could find images of. Having the seam bisecting the text in an uneven way also indicates a fake. It's odd to see text divided like that in packaging, but should at least be even if it does. On one side, it cuts just above the middle of the text, but the other side runs along the bottom of the text. That's a pretty glaring mistake for the manufacturer to make, but counterfeiters often make such mistakes. I could be wrong here, but still something questionable to me. If that is how the legit boxes are designed, then shame on Samsung I guess.
There's other signs as well, so I suggest you Google how to spot a fake S23 Ultra. Here's a link to get you started, but I found other posts commenting about the box too.
Don't get caught out, there's a number of these fakes circulating now. Please make sure even if it's a sealed phone you review my comparison of the packaging further down just to be sure. Even then to avoid being scammed always ask for the device...
xdaforums.com
I'd be tempted to flag the listing as a scam/fake.