There are other options. Especially in cases where requiring this is illegal, forging such a proof may be an option.
Or, answer “If I give you proof that my previous salary was X, I will precommit to only accept this job if you pay at least X + 20%”.
On one occasion I have said my previous salary but I also said that I believe I was seriously underpaid at my previous job, so I want X + 100%. At the end I have received X + 70%.
I had very good references though—my former student was a developer at that company, so when the boss invited him to the interview, he said “well, he taught me what I know” (which wasn’t literally true, but made a good impression).
There are other options. Especially in cases where requiring this is illegal, forging such a proof may be an option. Or, answer “If I give you proof that my previous salary was X, I will precommit to only accept this job if you pay at least X + 20%”.
On one occasion I have said my previous salary but I also said that I believe I was seriously underpaid at my previous job, so I want X + 100%. At the end I have received X + 70%.
I had very good references though—my former student was a developer at that company, so when the boss invited him to the interview, he said “well, he taught me what I know” (which wasn’t literally true, but made a good impression).