If I know that they changed it (and what it was changed with), I will wait a bit.
On my Santa Fe, it had 10,300 miles on it.
Dealer used Acura 5w-30 oil and a Mahle filter, so I left it in for ~2,200 miles.
I did another 2,500 mile with some Delo 10w-30 to get me to 15,000 miles (since I plan on a 5,000 mile OCI).
On my mom's Soul, it had ~23,000 mile on it.
Dealer used Mobil Super 5w-20 and an OEM filter, left that on for 2000 miles (got it to 25,000 miles for the same 5,000 mile OCI).
I know the Santa Fe was changed since when we did our first test drive, they had it on the lot for 1 day.
I checked the oil and it was a little low and dark (not nasty, just dark, and just below the full line).
The sales guy said the vehicle had not been prepped so before we picked it up they prepped it, which included an oil change.
Oil was nice and clear and at the full mark when we picked it up.
The Soul was a certified used from a Kia dealer, and that is part of the prep.
The filter was new (or else somebody washed the filter because it looked new) and the oil was clear and at the proper level.
For other fluids, depends on mileage and age.
Both of these were not that old with not a lot of miles, so the rest of the fluids stayed.
They will get transmission drain and fills @ 30,000 miles, as well as brake fluid changes.
Coolant will stay till the 3 year mark.