In addition to all the above suggestions, take a large flat blade screw driver and turn the 3 Zeuss fasteners on the top portion of front panel counter-clockwise so you can drop the control panel to take a look inside the guts of the control box. Wiring and connection points should look clean, not corroded. Check for any discoloration on wires/terminals, look for signs of any prior overheating/shorting of components, wires, etc.
Assuming the seller is willing to demonstrate it running, take something you can plug into the convenience outlet to verify 120 voltage/60-61.5 Hertz (~$35 Kill-A-Watt meter Home Depot). Check fuel lines for weeping. Open the Load Terminal lid (while its not running) and check to make sure all the brass retaining nuts are on terminals. Pull oil dip stick and ck level, BTW black oil is Ok...its a diesel. However, try to find out when fuel filters and oil filters were last changed. Also, ask if its ever been started using "starting ether"? That is a big no-no that could damage engine internals...rings, pistons, etc.
Its definitely been repainted. That alone would make me very suspicious that it has 27 original hrs on the Hobbs. Sometimes these units get repainted when someone uses a conglomeration of parts from multiple generators that were painted different colors (olive drab, desert sand, or camo] to make one running unit. Nothing terribly wrong with that if all "known good" parts were used to make one good unit.
What is date of mfg. and serial number? Beware that there are blank OEM aluminum placards being sold that anyone can stamp a fictitious date and serial number on to make it seem newer that it is. If you see the inspection stamp emblem then its legit, if not it may or may not be a legitimate placard. Tell tale signs are serial number is not perfectly aligned and depth of each S/N number punch is inconsistent. For instance, it could be a 1970-s era unit that is being represented as a 1991 (last yr of production).
If your not familiar with diesels, let alone this generator, it would be good to go to YouTube and watch a few MEP-002a videos so you get an idea of how they are supposed to sound and what the running exhaust looks like.