The real answer is that UBI isn't just money. Basic housing is free. Basic foodstuffs are free. In addition to everything else being sold, you can just get milk

The real answer is that UBI isn't just money. Basic housing is free. Basic foodstuffs are free. In addition to everything else being sold, you can just get milk. Or rice, or cheese. Or lots of things I haven't mentioned or thought of. No questions asked. It would be difficult to have predatory pricing if there's a suitable, free alternative.