Having gone through a number of these "residency" audits, I can tell you that there are all kinds of information that indicates where someone is domiciled. For example, drivers license, voting registration, real property ownership and exemptions, tax returns, utility bills, and a real beauty that I've got going on right now, credit card statements. All of these are "evidence" of where you live and remember the burden of proof is on the taxpayer.
In the example above it would even be possible that ALL three states could claim the taxpayer as being a resident and go after sales tax, income tax and even inheritance tax when that person passes. This was one of the issues when Howard Hughes passed away. He had many residences.