Just off of the top of my head, and you may already know this but if I was looking at them I'd look at where the pinion goes in, checking for breaks or cracks that would allow a leak or the pinion bearing to wobble. Granted you won't see anything microscopic but dents crushed or cracked.
Take a long look down it looking for bends in the tubes, almost like looking at a 2x4 at the lumber store. Look for damage in the housing, if the carrier or gears grenaded in there, there may be damage.
Mounts should look factory welded.
You don't have the luxury of all the rotating parts being on it to check for function.
That and direct questions spread out through conversation help find the hidden stuff. I always make small talk, telling "I had a buddy once..." stories then ask a direct question "are these mounts factory? " catches liars off guard and you can here it in their voice.
But then again when it comes to my money, I always think I'm getting screwed! But at 125.00 for the pair you are doing awesome and if you find out later they are junk, they are worth that in scrap.
Bring a magnet, there is a d44a that's aluminum from grand Cherokee.
I just bought a d44 complete and found a Dana/Spicer book that let's you run the numbers on the tubes (called a B O M #, bill of materials) and see what year it is, I downloaded the pdf and had it in the my phone.
Not saying you don't know what to look for, I'm just pessimistic about good deals, and always look for the hidden catch.