Not being a big storage locker buyer, I've not ever run into this situation. If the owner is there, they usually do not bid or are lousy people.
That said, I see it sometimes at estate auctions.
The saddest was the estate of an old woman. She had suffered some sort of ailment (I don't know what, but as she wasn't dying and was of sound mind, I assumed a fall or stroke) and had been put in a nursing home by her family, who then took her items to the auction. The auction had 20-30 booths, each with items from a different dealer/merchant/owner and 3-4 auctioneers going down the line.
Sometimes at those places you end up talking to people. I found myself talking to the woman's friends, who were also elderly, likely living on SS and had little money to buy some of this poor woman's things. She didn't want the pricier items, just family photos, her old toys, etc. A few of the bidders (including myself) either bought the things for them, or ended up buying group lots of items and let them pick out the things they wanted. None of it was traditionally valuable stuff, not even for what it was. It was old rag dolls that go for less than $40 at flea markets, etc.
I do think they got most the things the woman wanted back, but it was still rather depressing. Imagine your family being so lousy that they don't even let you pick out personal items and you have to send your elderly friends to pick things up for you. That's when you cut the kids out of the will!
I suppose the kindness there comes in that bidders were willing to help them out.
Other than that, I recall seeing one man who was in his 60s-70s selling his mother's belongings. Apparently she had only recently died in her late 90s, and he was literally crying as he sold her items. No clue if he needed the money/space or just couldn't deal with having her things around due to the memory. He made a point of telling everyone who bought something the "story" behind it.
Nothing you can do there, but it was still sad to witness.