It varies. I work for myself. Recently when I was working at my startup and took a salary I made ~$120k/year. When I was contracting I made $150k-200k/year. Recently I moved from San Francisco to Yangon, Myanmar and haven't been working much. So far this year I've only made $12k (which is enough here to live for a year).
If I wanted to purchase a house I would pay for it in cash, so I don't need a loan. I don't buy things I haven't earned (crazy! I know). I don't use debt. I don't have to worry about what a lender thinks of me.
As far as mortgages go, I know someone else who doesn't have a credit score and got 3.5% using a manual underwriter. If you have good finances you can get good rates without a credit score.
