I am with Sott P. on this one. Safety first, always. If I cannot see where my foot will rest I don't walk joists. An inspector friend of mine in the Dallas area spoke with a man at Home Depot in passing one day and the guy's son-in-law had been a home inspector. He was electrocuted to death when he was in an attic and walking across joists covered in insulation. He never saw the bare splice he put his ankle against that was lying on top of the joists he could not see because of the insulation. It gave me a new perspective on attic inspections.

Each inspector is different and has their own methods. Unlike J.P. I have stepped through a ceiling on an inspection and when I was contracting prior to becoming an inspector. It can be dangerous and can be expensive to repair. (Not to mention the injury to your pride.)

If I can see the joists and feel that I can safely walk them (three point as stated before) then I will sometimes do it. Every house is different.

Disclaim with explanation anything you cannot inspect thoroughly. I do not take chances with my safety. You cannot inspect thouroughly at all if you are in a wheelchair or worse!

Eric