Will BRRR fail if there are more rentals in supply than demand?

[Leo Poon]

The whole process of BRRR is to rent out the units and get refinanced, then repeat. But what if the markets have more rentals available in supply than there are renters who need to rent in demand, so you are stuck with a house with no tenants. I know we are supposed to analyze if the market we are investing in has more rental supply or more demand. Question is what metrics or data do investors use to analyze if the rental market has more units available than there are renters. Also, is there a DOM for renting instead of selling that could indicate it will take longer to rent out a unit in certain cities?