Home Inspectors follow the standards of practice of either ASHI (American Society of Home Inspectors), CAHPI (Canadian Association Of Home & Property Inspectors) or InterNACHI (International Association of Certified Home Inspectors)
All three standards call for an inspector to check a “representative number” of electrical outlets. But what exactly is a “representative number”? It is rather vague. I have heard some inspectors say it is one outlet per room.
I say ALL outlets that are available should be checked. If an outlet can be seen, and is not obscured by furniture or belongings, and if it does not have something plugged into it, then it should be checked, because you never know.
A case in point is this bedroom of a cottage near Brackley Beach, the first outlet I checked was fine, but all of the outlets on the outside walls had an open ground. Had I only tested the first outlet I came to I would have missed the other 4 outlets with problems.
Choose an Inspector who tests all available outlets, and not just a “representative number”.