1) I am thinking about a web-app for now.
2) eBay's private listings is different. All the users can bid in an eBay auction. In eBay's private listings, just the username is kept confidential. Whereas with my app, only the users invited will be able to bid.
You talked about element of trust/enforcement. The one who is creating the auction is inviting people by their email. So, he will invite only those people who he trusts.
You talked about element of trust/enforcement. The one who is creating the auction is inviting people by their email. So, he will invite only those people who he trusts.