You can check the documentation, permit info, warranty etc. or often there is an owner’s manual inside the home and also a plaque on or near the inverter or one of the switch boxes with the company name and contact info.

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

Retain all copies of documents you got from them as evidence. 

Once it sells your qualified intermediary can provide all the documentation needed for the lender.

Make sure you document well your interactions with the tenant.

Some say it’s possible to implement this strategy in Germany, while others claim you can't, due to regulations preventing the sale of mortgaged property before 10 years.There's a lot of confusion and misinformation, and no one seems to have solid information.This strategy is well-documented in the USA, with numerous videos on YouTube.

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

We strong suggest to always get a Real Estate Attorney to review all documentation and prepare the seller docs (do this always - even if you have a Realtor).Most BP members are experienced enough to feel comfortable doing this themselves ... after you do 2 or 3, it will become routine.You are saving thousands of dollars so you will need to do a bit of work yourself, but it is worth it.Never pay full commissions any more ... if you decide to get a full service Realtor to list your house, that is fine (the Entry Only concept is not for everyone, we understand), but always negotiate a flat fee. % commissions are not valid any longer ... what additional work does a Realtor selling a $600,000 has to do than to sell a $400,000 that is worth $6,000 more in commission?

If you decide to use the property as a second home, 90% financing is available on a full documentation loan. 

There's a contract in place and that decides who gets paid what- you don't have to like it or think it's fair, but it's a binding document.