Earlier quoted context omitted.
They can't legally ask for proof, no. Bluff away! (I'm not a lawyer and this does not constitute legal advice.) I did a small bluff to try it out, just 5k above what I was making. The recruiter was surprisingly skeptical! I know I've done an good job of bumping up my salary in a short amount of time, but it was kind of off-putting to have him question it.
> They can't legally ask for proof, no. Bluff away! Well, I am a lawyer, and this is also not legal advice. To lie and accept a job offer whose salary is predicated on the lie would constitute fraud. Lying about your former compensation history is no different than lying about a prior criminal record, if the counterparty relies on the false assertion.
Disclaimer: Not a lawyer, not your lawyer, but fairly confident based on past experience with this over ~15 years.