Was 4WD not engaging or something? Is the seller a private party or a dealership? The transfer case motors can sometimes go bad (speaking for ALL F150s, it's not a raptor specific issue btw). While confirming 4WD status, doublecheck IWEs (holes in vacuum lines are a likely culprit), etc - can read up more about that if you are new to F150 / raptor platform.
There's only a few "gotchas" that are specific to the truck (fuse 27 among them), can search/look up past threads, browse maintenance section, etc for more details while you are waiting for the truck to finish being looked over/serviced.
Here's an official chart from Fox btw RE their recommended service intervals: