For engines there are a number of checks/tests i.e. compression, leakdown, oil analysis that may give a potential buyer a good feeling.

What about outdrives ? I'm thinking the following :
Check oil for water and burning/overrheating/discoloration
Check magnets for metal fragments
Check engagement to forward/reverse
Listen for unusual noises
Check prop shaft runout.

Are there know things to look for in a III, IIIA ? I've recently seen some boats with III and IIIA's which I've not considered in the past and I'm ignorant of these drives but understand they are very expensive to repair.

thanks,ed

drain a little fluid from the drives look for metal/water, rotate the prop shafts and listen for noises

And maybe pressure test it to check seals.

Send to Randy @ Marine Drives for yearly inspection if
your running big power. You can listen all you want &
turn the shaft but a 15$ bearing can cause you Big$$$$.
That goes for any drive.If your running 500 to 700 H.P
on 3as you can go about 100hrs. Jusy My 2