I would without a doubt recommend a larder deposit then 10%.. heck that's less then arbitrage in some instances. dare i recommend 25%? sounds high. however in the matter of the time it takes for bank transfer happens a lot can happen in the markets. Alice would get screwed if bob has greater incentive to walk away from his deposit if he has a better trade opportunity.

in a different scenario
 there might be a chance bob could extort Alice in order for her to get her deposit back.  should he refuse  to confirm

yes this is what i was getting at..

What happens to the flow of money under the following scenarios?


Bob claims he never received fiat funds?
I'm not worried about the reverse case as there no question about bitcoins going through.


alternative scenario.
Bob dies in a car crash on way to work before acknowledging receipt?