I would be very cautious if the oil has been recently changed, if the oil looks brand new it is a big red flag. Looking at the oil tells a lot of stories. Also like said above it it has been cleaned to look brand new. Like said above run test, load test.
When I buy a used vehicle if I look at the engine and see a nice steam cleaned engine with fresh oil in it, I will generally walk away unless I am prepared to rebuild it.
Yellowish and creamy or worse foamy; it has water getting in
Sparkles; bearing or ring, or piston scrapping. They could have let it go low.
Extremely black; rings getting bypass
Sludgy; they didn't take care of it.
Smells like gas; rare but a leak somewhere.
Be very cautious when buying used.
2014 Arctic Fox 30U
2001 Silverado 2500 HD, 4WD
8.1 Vortec / 4.10 gears / ATS Stage 2 Allison Transmission with Co-Pilot
Tekonsha Prodigy P2 Brake Controller
Reece Class 5 Hitch with 1700lb bars