Two searches deserve your top bid and neither one contains the word rental
The clicks that become agreements come from an owner with a problem and a deadline, not from anyone browsing the category.
First is the owner with a start date somewhere else. A house in Highlands Ranch or Littleton, a job in another state, and a decision between listing it and renting it. Their searches mix the choice itself with cost questions about what a manager charges.
Second is the owner already under contract with a firm they no longer trust. Late statements, a long turn, a tenant calling them directly. Those searches carry competitor names and words like reviews and complaints, and they convert at a rate the category term never will.
What the two share is named intent plus a place. Bid those to the top of your range. Everything broader gets a ceiling and a short leash.
Investors with several doors are the highest value and the thinnest volume. Give them their own ad group and their own copy, written about reporting, fee structure and how you handle a portfolio, not about peace of mind.