I picked up a JDM Nissan SR20DET 10ish years ago and had a good experience with that particular vendor and engine. I had it apart years later and the bores looked like they matched the stated mileage, really nice shape.
Lots of horror stories out there, though. I felt more comfortable with a vendor like you posted who had a stand alone website and business outside ebay, just felt like name recognition was worth something.
One tip is to find someone local-ish or see if you can make a longer drive or combine with a vacation to pick it up yourself. They tend to get crates of engines at a time and if you just buy it online or on the phone they might send you the nastiest looking one since some other customer is coming in to pick one up that needs to look better. I did this, drove 300ish miles to the importer's shop and it was totally worth it. 3 engines sitting on palates and I got to pick whatever one I liked for the same money. Couldn't compression check or anything but you can tell a lot just visually. That means two other customers got relatively junky engines without knowing any better. Think of it like a puppy
My engine did come with a cylinder full of coolant which seems really common. Likely from when the heated throttle body was removed and it flowed in through an open intake valve. I would say at a minimum make sure you pull plugs and spin it over to blow out any water before cranking with plugs in. You would probably be well served to just throw a head gasket at it and take a look around the chambers since that's pretty easy when you've already got the long block on a stand.
Long story short, it's a bit of a gamble but the price is usually good enough that even with parts to fix something unexpected you're still in the black.
Alex