Given that they are never going to go to your previous employer and ask them what you made, there's nothing to lose there. Anyone who does ask something like that isn't someone anyone wants to work for anyway.
Always add 10-20%. If they like you, they will offer you and you can negotiate from there.
They don't get the info from your previous employer, they get it from your previous payroll processor. Many payroll processing companies happily sell your financial history, which is made available to your new employer via most background check companies.
Always add 10-20%. If they like you, they will offer you and you can negotiate from there.