That’s not red, blue, or purple, just the reality of more investors/listings in the mix than we had 3-4 years ago.Quote from @Bruce Woodruff: Quote from @Cliff H.: And looking 5 years out I fully question whether STRs will continue to show greater returns that MTR/LTR rentals, particularly those rentals already focused on niche markets for better returns. 

Even if I can remodel, will there be any red flags holding this quadplex as long-term rental units?

Also, would like to hear if anyone has used Red Door property management and what their experience has been.  

If they can't or won't do that then it is a red flag for me as a property manager. 

I am not interested in going any further.Definitely alot of red flags for sure. 7 days is short notice, but i'd also reach out to AirBNB to cancel because your "uncomfortable" with the reservation.

Especially if the property isn't/wasn't habitable.One call from the tenant to code enforcement can cause you month's of red tape, bureaucracy, hearings, and expenses. 

If you want to watch the full presentation you can do so on my company webpage, but the highlights are this:RE Lenders require collateralRE Lenders require "Skin-in-the-game"RE Lenders ALWAYS mitigate risks, the primary way they do this, require more "skin-in-the-game" from the borrowerIf you ever find a "lender" that uses a "free" email service this should be a huge red flag. 

Should it raise any red flags?

This can be a major red flag, because it probably isn't your intended use, it may not conform to zoning, and it could result in increased wear & tear, complaints from neighbors, and code violations. 

Sounds like a lot of the red tape is focused around not making any drastic changes to exteriors with these historic homes.