Actually audit you and require proof? Both California and New York will do this.
https://www.latimes.com/busine...
"Answer: California, like other higher-tax states, has residency auditors whose specialty is asserting that affluent people who have left the state are still legal residents and thus are subject to its taxes. The audits can be stunningly thorough, looking at everything from the doctors you visit to where your artwork and other valuable possessions are stored.
If audited, you would need to prove that you have a fixed, permanent residence elsewhere and that it’s truly your home. And yes, it’s up to the taxpayer to prove this — there’s no presumption of innocence in tax audits, says tax attorney Mark Klein, chairman of Hodgson Russ LLP in New York City. (New York is another state with notoriously hard-nosed residency auditors.)"
https://www.sambrotman.com/per...
"If you have decided to relocate to another state to escape California’s high tax rate, then you need to do so with caution. Or, maybe you divide your time between California and another state(s).
The state is very aggressive about collecting state income tax they believe you owe, and trust me, they will track you down.
Many of our clients have had their residency challenged when it comes to filing their taxes. The Franchise Tax Board (FTB) will scrutinize your bank records, records of purchases and other transactions to make their case that you, indeed, are a resident of California. "
https://www.hodgsonruss.com/wh...
"HOW LIKELY IS IT THAT I WILL BE AUDITED?
Very likely. If you are a high-income taxpayer claiming a move into or out of New York, it’s a near certainty you will be audited. The Tax Department is sophisticated and aggressive. Consider some of the numbers:
The tax department has ten district offices located across the State (and in Chicago).
There are more than 300 auditors who focus on these
Over the past five years, the Tax Department has conducted over 15,000 of these
These audits have generated over $1 billion in revenue over this time
In short, there are a billion reasons why the New York Tax Department watches these issues carefully. If you claim a move from New York, expect to get audited."