I think the key here is
communication .
Personally, I have been in this situation several times, and prior to finding my way to GC!
I've had eBayers (who happened to be sisters, as I would find out) email me as high-bidder to tell me why this item was important to them. Had they simply said, "I want this", I may have been inclined to respectfully tell them that I also want it, let she with the deepest pockets win! (I mean, if we are just talking 'want' there is no gauge for who should win.) I've also contacted a competing bidder, to ask what her interest is in the item, only to receive no response, or worse, a very rude one! ("Yes I am a sister, not that its any of your biz, and I want that item and I'm not letting you win!" - words to that effect. Nice, huh? Yeah, that compells me to back off - NOT!)
However, these eBayers who could express a sentimental reason why the item had meaning to them (an item from their chapter, replacing a similar lost item, etc) which as a Sister, I respectfully let them win (or exchanged for cash if my bid was way high...).
Ebay is a free market, but we should act as Sisters, respecting one another. I don't think we could really create any policy, only the guidlines to Communicate with competing bidders and the Respect your sister!
That's my $0.02, which was really more like $2.00, but keep the change.
[/soapbox]