Sounds like you called on my tenant occupied listing.
The tenant DID NOT agree to any showing schedule and DID NOT answer or respond to my calls.
Although my sign with image was on the front lawn, when I stopped by to inquire about activity, she did not recognize me and responded, "The agent has never called me." Needless to say. I was left without words.
Meanwhile, other agents and buyers are piling up, awaiting the opportunity to see this home.
When access was granted, the one and only day the home was shown, the buyer was able to overlook the 'hoarder' attributes and made a purchase offer that was accepted.
There are many reasons a tenant will not cooperate. Unfortunately, all blame is placed on the agents involved, just as your question does.
Further, when I encounter buyers whose intent is to blame, not participate, they are never invited to the negotiation table.