> Even in UBI, there would be a strong expectation that each person only receives it once. But checking stuff like that requires a huge bureaucracy.

Or you issue UBI all at once during the month, and you stamp everyone who receives it with an indelible ink mark that takes longer than a day to wear off; like they do in poor countries to prevent double voting.

It's a solvable problem. The problem is that the "cost of managing welfare" is a small percentage of the cost of welfare, you can't pay for doubling/tripling it by saving 5%.