This is why it is important to explore the zoning and the history of the property to make sure you do not purchase an illegal property.

Can I see the payment history? 

Verifying last 2 years of rental history very important!

What documents do they require, what credit scores do they allow, how do they verify previous rental history, etc.?

My experience 1 investment 200 thousand in self storage in Germany have been receiving average cash-flow of 10% over the 7 year history and that does not include the asset value of my 200 Thousand dollars today estimated to be around 500 thousand 

Verifying last 2 years of rental history very important!

What documents do they require, what credit scores do they allow, how do they verify previous rental history, etc.?

Another thing is that Zillow and Realtor show the price history so buyers can see when you bought it and what you paid for it. 

Are you using a servicer to track the payment history ?

If the property has STR history and this is your first time buying an investment property you may also push for an exception with a higher downpayment 25-30% along with other compensating factors.