Any advice on buying sets second hand?

Hello,

I will be buying a Lego star wars UCS set second hand from someone from work in a few weeks. I'll be doing so because he's giving me a crazy good deal on it.

However, I am a bit apprehensive about doing so. I'll be spending a lot of money on something that I'm not sure is going to be complete (tbf, I've never heard of an issue from buying things from people at work on our selling channel). The guy told me that the set is new in box so I'm hoping he's telling the truth.

Is there anything obvious that I should watch out for in terms of inspecting the set? Only things I can think of is making sure that the tape that holds the box together is correctly positioned (already went to my local lego store to see how the tape is arranged), and opening the set and counting each individual bag. I was able to find a post in this sub that contained the spread of bags and their numbers, but I'm not sure if the guy will let me inspect 66 bags and open all the boxes right there and then. Also don't wanna ruin the unboxing experience for me, but hey, you gotta do what you gotta do.

Any advice?

Thanks!