After you've decided you still want to deal with them, call the financial institution that provided the proof of funds to the buyer. 

This is considered being "arbitrary and capricious", they have rules adopted, if you follow them they can't deny your application- otherwise what's the point of the rules? 

@Mack Lengel most folks on here are investors...and do not have a background in either hospitality nor are they institutional smart-money with unlimited capital.

PS, I always am polite on my offers, sometimes impersonal offers make people feel like they're dealing with a institution vs a human, If they feel like they're being bullied they may stand firm.

Easy way to look at things are any institutional, or Hedge funds buying in this asset class.

Not only do banks do the loans but some IRA owners prefer t0 do  loans than owning the property- but either way it must be non recourse.To set up a SDIRA is easily done within 48 hours, getting the money transferred is approximately 2 days to 4 weeks dependent on what institution it comes from.  

But many things can cause your vacancy to skyrocket - economic downturn, a Cat 5 hurricane could take out the local infrastructure for years, local governments could adopt anti short term rental policies, etc. 

While 99% of banks and institutions would not loan to someone with no income, you MIGHT be able to talk a hard money lender into loaning on the property.

How likely are you to adopt such technology at this point in time?

I have looked over the HUD guidelines and am still unclear about whether I can institute these guidelines.I also would like to find out of if I can require that the tenant's rental insurance include coverage for dog bites.