UBI is implemented tomorrow. Every citizen gets $1000 per month.
Landlord now knows you have an extra $1000 that you never had before. Why wouldn’t the landlord raise prices?
Now you have an extra $1000 a month and instead of eating rice and beans for a few meals you go out to a restaurant. The restaurant owners know everyone is eating out more so why not raise prices and maximize shareholder profit as always. The restaurant/corporation is on TV saying, “well, demand increased and it is a simple Economic principle that prices had to increase. There’s nothing we can do about it”.
Your state/country has toll roads. The state needs money for its deficit. UBI is implemented and the state/country sees it as the perfect time to incrementally raise toll prices.
Next thing you know UBI is effectively gone because everything costs more and billionaires keep hitting higher and higher all time net worth records.
A negative income tax system has the same incentive as our current bracketed tax system to earn more money: for every dollar you earn, even if a higher percentage gets taken out on that next dollar, you still have more money now.
It just shifts our brackets down so that you get “negatively taxed” - given money - for the lowest brackets of income. But a person making $100k would still be given say $15k for the first $10k of their income, $5k for next $10k, taxed at 9% for the next $10k, 20% the following $10k, so on and so forth - so that every dollar they make still means more money in their pocket, it’s just a percentage less for the additional dollars as they move brackets. Considering that’s already how it works, it seems no incentive changes would arise for high earners.