Many years ago, when I applied for my first mortgage in the UK, the most I could borrow was two-and-a-half times my annual income, or three times my and my partner's joint income.
The restriction on how much we could borrow was strictly enforced, so mortgage hunters often had to think of every penny they earned in tips, commission, bonuses and any ad hoc work they might do to get the biggest loan possible.
And although almost any figure could be declared, it wasn't unheard of for the bank or building society to want proof of income -- by way of payslips, tax forms, or bank account statements.
You also had to declare any loan repayments, and having a credit card could reduce the amount that you could borrow.
The system had two benefits. House buyers could rarely borrow more than they could afford to repay every month, and sellers knew their buyers were limited to what they could spend.