1. It's hard to see how guaranteed income would put the less well off more at the mercy of the well off. And you don't provide a causal explanation of how this effect would arise.

2. Surely UBI is cash, not vouchers. At which point the particular lower-than-face-value scenario is moot.

3. This is a valid point. I'm not sure whether it's good or bad, but it does seem likely to entail some morality shake-up.