Hopefully, he will change.If his behavior continues, write a letter communicating the same.

Cap rate is a market-driven metric, which measure the attitude and behavior of all market participants.Here is a BP link I think will help you better understand:https://www.biggerpockets.com/renewsblog/2016/05/31/cap-rate-formula-include-debt-service/

I just finished my Doctorate (I'm 26) and am working as a nurse practitioner and quickly realizing that if I make this my entire life I'll end up on the other side of the locked psych unit (I work in behavioral health).

I fell into this behavior with my very first rental property where my tenant took advantage of my kindness and 2 days late on the rent turned into 2 months behind in the rent and I ended up having to evict the tenant.

If this is repeated behavior or you have caught them in a lie that is a different story.  

You can syndicate anything but let's say you do MF apartments since that has been a strong wealth creator that has earned its stripes and offers a favorable future based on a number of demographic, economic and behavioral trends. 

Plus fresh water, moderate summers and generally high quality of live is already changing migration behavior.

Check your state law because some states are starting to regulate this.Credit score is still the best predictor of future behavior available to most Landlords and you should absolutely consider it.

Is that ethical behavior for a licensed broker?

Buyer sentiment is not improving and with 2008 being the only memory of a housing crash to a good portion of the population, their behavior is likely to lead them to sit and wait further eroding buyer sentiment.