Regarding reputation - the theory would be that you would be willing to accept transactions (that were on the blockchain, of course), from a particular wallet,

Regarding reputation - the theory would be that you would be willing to accept transactions (that were on the blockchain, of course), from a particular wallet, after that person had some type of reputation (either because they had provided identification, or had a track record, or some other method of proving that transactions from this wallet don't always have to be confirmed three times, particularly for small amounts of BTC. But I think your system would work as well - but it then needs more than just a bitcoin transaction from my wallet. I'm just trying to think of how we can encourage Restaurants and Grocery stores to start accepting BTC, without getting scammed by double-spends.