as you said.. depends on the particulars of the flood.
if it was driven into a lake and the engine did not hydro lock, and they pulled it out, drained oils and refileld and went.. it might be completely fine.
I bought a ford tractor post katrina, from lousiana. unit had been UNDER the high water mark
when i got it home, I took everything off I could, and flushed sumps. it was a bit of a rare ford or I would not have went for a drowned one. it was an offset. and the price was right for one that went swimming.
i pulled the final drives, pto shaft, trans cover, hyds, engine covers.. etc.
repacked wheel bearings.. etc.
I found fine silt in the final drive pans and almost all sump bases. not like piles of sand.. just a silty fine. the hyds though actually had some plant matter and more than silt, in it. the lil connecting tube onthe hyds the offset used was actually plugged with dirt/debris.
wheel bearings were loaded. engine looked good. side covers and valve cover were about what I normally expected. looks like turbid water and silts stayed lower than the engine top.
all the gauges were flooded.. I was surprised the genny and starter cleaned up, but they did.
pto shaft beairng shad actual sand in it.
it all cleaned up after about 3 weeks of work... tractor ran and started fine after that.
-if- the owner of yours took the time to mitigate the issue.. it's likely fine.