Yes I would have wanted to change the oil/filter/preoil/oil the cyls. He might be aggravated at all the lookey loos he's had to deal with down the line which I understand (especially after dealing with CL
). I would have turned the crank with a 1&1/4" socket/ breaker bar & if it turned then I'd be OK with it. It's a moot point now & not sure why he's getting PO cuz you certainly did not lie you just wanted to take precautions. He might just be a hard case & wants you to close the deal. If he gets too nasty he'll end up queering the deal & running you off. Get it home/prep it/fire it up/post some pics
. I'm assuming it was not started so you're still in good shape & you can now do the prep you wanted to & no damage to speak of was done just by it being cranked over assuming there is no rust in the cyls.