And how would UBI change that? The kind of people who are willing to break the law to avoid paying taxes are already breaking the law to avoid paying taxes.
You're reiterating my "UBI will be miserly" point. Yes, if taxes were set at 100% to support a $40k/year UBI, I would quit my six figure job to make $10/hour cutting grass under the table. OTOH, if my taxes went up 25% to support a $10K/year UBI, I wouldn't.