I'd say the line gets drawn between landlords that do physical labor to maintain their properties and landlords that outsource the whole process to someone else.

In the first case, the tenant is paying for real labor. Landlords that handle their own drywall and plumbing. Landlords that mow their own lawns and fix their own appliances. Handymen that own a property or two and maintain them as part of their trade. These landlords exist, but they are few and far between. I mostly see them at Airbnb properties and small family-run motels. But even that is going by the wayside, as investment clubs and lending groups either buy them out or run them out of business.

In the second case, the tenant is effectively just paying a vig to the landlord in order to access the landlord's low-interest line of credit. These landlords are fucking everywhere. All your big corporate offices - your Amli's and Lincoln Properties and Pinnacles - effectively operate this way. They've got legions of (routinely underpaid) staff and subcontractors who actually do the work of maintaining the properties. They kick back sizable chunks of their revenue as administrative overhead and - in the case of publicly traded firms - dividends and stock buybacks. Only a fraction of the rental income goes towards the actual acquisition and maintenance of the property itself and the properties are regularly leveraged out for more new borrowing power used to gobble up more open real estate to add to the cartels' portfolios.

The second group also tends to get significant tax incentives, subsidized loans, and other forms of funny money, allowing them to operate for short periods of time at a loss in order to squelch independent competitors.

The real line is ultimately the ROI on the property. If you're earning a standard workman's salary off maintaining a second unit, I doubt anyone will seriously bat an eye at your habits. By contrast, if you have title on a dozen different multi-million dollar multi-family units and you're clearing double-digit annualized returns in what amounts to a part time side-hustle, that's a pretty clear indication of price gouging behavior.

But because price gouging in the real estate market is so routine (to the point that "buy a home" is common wisdom, entirely because its the only consistent way to escape predatory rental practices) we've stopped acknowledging this method of usury as anything but normal.