Basically, check all systems for proper operation...and inpect everything for problems or damage.
Some things you may find after delivery, and may still be under warranty for some time if it's new.
Sometimes, it helps to bring another person to help look things over...especially someone with RV knowledge.
It also helps to ensure the seller shows you how to work everything.
Pete (Jolly Mon)
2018 Wildwood Grand Lodge 42 DLTS
-Seasonal Space, Northern MN.
-2017 Sylvan 8522 LZ LES/115 Merc/Sea Legs