You just described a "negative income tax", which isn't the same thing as UBI.
A negative income tax is exactly the same thing as a UBI in a system that also has progressive income taxes.
If it was gradual withdrawal rather than a cliff, she could afford to take the job.
The UK's Universal Credit is supposed to be gradual and therefore work out to everyone's benefit. But in practice it has few of the good qualities of either UBI or negative taxation. Universal Credit has plenty of nasty cliffs, complicated rules and cruel penalties that push unlucky people deeply into poverty, and it also has an extremely heavy administration cost - every employer must file everyone's individual employment taxes every few weeks online and face heavy fines for getting anything wrong or being a day late.
If it is self-defeating, it is not more efficient. And we already have a bureaucracy whose functions include verifying income claims and adjusting net payments based on them in the income tax system, we don’t need a bunch of different bureaucracies doing that redundantly with slightly varied definitions and rules and paperwork that serve little practical purpose besides justifying additional bureaucracies and enforcing self-defeating funding cliffs.
It is possible that there would be fraud around pretending to be a person when that person doesn’t exist, or continuing to collect benefits for someone who is dead.
But “are you a live person” is much harder to fake than “did you make sure you didn’t do these 6 illegible things that would make you ineligible”.
When you eliminate means-testing in favor of income taxes and eliminste the myriad different definitions of income and assets for qualification for different programs and the opportunity it creates (and the incentive funding cliffs create) for specialized benefit fraud, there is no special “UBI abuse” to monitor for. You have to monitor for tax fraud, but we’ve got a bureaucracy doing that at society-wide scale anyway.
UBI could be a solution but has its own drawbacks. Progressive taxation without cliffs is another possible solution.
That is, you pay higher taxes but only from the amount above some threshold. That way, only the derivative of the tax rate has cliffs.
You mean with no public support? Because UBI is social support without cliffs, and typically paired with progressive taxation. So if you mean progressive taxation with social support and no cliffs, that's not an alternative to UBI so much as a long-winded description of UBI.
> That is, you pay higher taxes but only from the amount above some threshold. That way, only the derivative of the tax rate has cliffs.
That's (ignoring things like the injection of means-tested welfare into the tax system via EITC) progressive taxation and tax bracket marginal rates work normally. UBI is just adding public benefits in without introducing cliffs.
The problem with means testing is that it effectively raises the marginal rate, often to astronomical percentages. For example, the withdrawal of a $1000 benefit because of an additional $1 that pushes you over a means testing threshold means your marginal tax rate on that dollar is 100,000%. Of course the rational thing to do is to not earn that dollar, or indeed any of the next $1250 that it would take to get you back to where you started (assuming a normal marginal rate of 20%).
For example, a reasonable stepping stone would be for people to get their food stamps by default, but then be able to "pay" some of the taxes on any income they earn using those food stamps. This means food stamps are being reduced gradually and at the marginal tax rate, so it's fairer than just falling off a cliff when you hit a threshold.
In a mature UBI system [0], food stamps as use-restricted means-tested welfare wouldn't exist at all. (Food stamps in their original purpose as a system of agricultural subsidies might.) Their function would be rolled into the single benefit payment.
[0] transitional proposals often keep other means-tested programs during the transition, scaled back as UBI scales up.