Just sent them a rent increase notice every year.

Your not correct under many different circumstances.First property tax is 1.1% (fairly safe) with 2% annual increase (prop 13).Next expenses include a lot more than property tax and interest. 

They all left at the first sniff of an increase despite still being below market and they were all pretty upset about it.

@Jadan WilliamsIf I were in your shoes, I’d start by clearly defining my investment goals and identifying target markets with strong job growth, population increases, and development potential.

You really have to learn the neighborhoods or work with a sales agent who does.

Despite no additional renovations being necessary, our efficient strategy and swift turnaround led to a same-day sale at $225,000.

A high property tax rate will increase the taxes more quickly as a percentage of total expenses when the property value increases.

Eventually, Class A property values increased to the point that even increasing rents didn't allow them to cashflow upon purchase.So, the flood of new investors switched to buying Class B properties.

Trust invests the cash to make the payments on the installment sale to the seller.

As they see their money is safe and you're succeeding with your plans, they'll usually ask to increase the amount of money they loan to you.