While I have no experience with radar locating devices, I can only speculate that the tool requires a fair amount of interpretation and training, like any diagnostic imager.
You want to devote that much time to an ancillary service? Are you going to start scanning a client’s yard looking for abandoned tanks? And then what do you do if you locate one? Are you going into the tank removal business too?
I’m sure your area has valid reasons to find and locate the underground fuel tanks for proper removal, but I can’t see that being an adjunct to home inspection, rather a stand alone venture that requires a large amount of resources such as time & money. (Which is fine if that’s a direction you want to go, but I’d focus on your core business first-home inspections.)