For example, if I return a screwdriver to Lowes, it counts that as revenue.

I would take it a step further if you can and join a Mastermind group, cost is fairly low, but you get so much knowledge and meet so many investors that are doing all sorts of deals.

I personally want to use this strategy to lock in a lower interest rate on a rental property (being 20 years old with a small amount of credit history). 

I will have a property or 3 that I've located,  found owner negotiating seller terms,   knowing I don't have the credit or capital or network for sourcing either,   I'd go to sites or platforms that want partners for 50 50 deals..   

I have had a few recommendations for credit unions in the area with great programs, but because my primary residence is in Florida I do not qualify for membership.

I was getting interest rates that were slightly over 7% for a fixed, and I recently learned about the 5/6 ARM through my local credit bureau who I had financed my car through many years back.

Roberto, yes, I can pull from a line of credit to pay it off with short notice if needed.

If not, generate cash and build credit profiles for free i.e. 800 FICOs and 80 PAYDEX LLCsbecause when you need to raise money, the more options the better.If you need any advice on building credit effectively on the cheap,feel free to reach out :)This is my opinion and I'm not licensed,John Acheson, MBA

Bought right before Covid with low(er) prices and low interest rates.

You’re talking a low dollar entry point.