The same way you can continue to afford your house payment. Simple math.
She bought this house new in 2015 for $787,000. From what she told me, she pays 50% down on all her rental homes in cash and gets interest only mortgages on the remainder. She usually does 5/1 ARMs. So, she refinanced the loan balance in 2020, probably at a super low rate. Her monthly mortgage payment is probably like $1500?
Taxes on this house are about $12,000/year. So that is another $1000 per month. So now we are at $2500/month.
Insurance on a rental property is low. She probably pays like $1500/year for that. So let's say $125/month. HOA fee is $135/month. She pays the trash/sewer fee which is around $50/month. So we are at $2810.
Maintenance has been basically nonexistent since it is a well built newer home. She has had to outlay, I'd say, $2500 over the last 8 years in total on various issues that have come up. I know because I pay for the repairs initially and she reimburses me.
So let's round it off to $3000/month.
Initially, our rent was $3250 in 2015. It is now $4200 starting next month.
She is still turning a profit. She was always turning a profit. But she isn't using these houses to generate profit NOW, she buys them low and sells them high. In 2015, she bought this house AND an identical one a few blocks over. Each is now worth $1.3 million dollars. She could sell them right now and realize a $1M return on her initial $800k cash investment. That's her end game. She has 7 residential properties and 2 commercial properties. She lives in Boston and has these properties spread around Boston and Southern CA. Once they skyrocket in value, she sells them and uses the cash to buy the next one. She mostly only buys high end new construction and sells them before they start needing extensive repair work. She has been doing this for 30 years.