30psi is close to the end of the world in outboard terms :-).
there is something amiss in that top cylinder obviously.
i'd rather have 3 cylinders the same at 90psi than the readings you got.
running ok is relative, i think your not running ok which is a result of the PSI reading. your probably losing a good 3/4knots and 500rpm with that reading.
will the engine work for someone pottering about-yes without doubt. however it still doesn't change the fact the motor needs pulled apart if the owner cared. it is only a matter of time before whatever it is becomes terminal and it will no doubt be in the middle of nowhere it happens and not going back on the trailer.
btw i have had an engine before like that, funnily enough a suzuki 85 the same model as yours. after winterisation i had lost about 5/6knots, upon inspection with compression tester the top cylinder was about 35 psi off. took the head off and seen a crack-i.e the end of the world! :-(.
enjoy your new motor-take the compression gauge with you when buying and trust me, not your outboard dealer, if the PSI is 5 or so of a diff then walk away :-)