An extension of this would be to bring in third parties as proxies. Then you could see bidding, on R, on I, on the proxy fee, or any other parameter. This would be a pain if it required human intervention, but presumably could be automated. In the limited-trust scenario you describe, maybe this sort of thing could bootstrap the rest of the banking system?

Considering that most confidence artists gains the mark's trust by first opening themselves up to him, using R 3 would be classic setup for a confidence scam.

Knowing that the Risk is growing each round, the con artist stands to run off with a large chunk of money on the last round.

Ultimately, the "trust" gained from successful transactions at the early stage isn't bankable.

So the system still depends on the man with a gun (arbitrator) to enforce it.