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

If the police came they probably did not come and document the damages, get the report.   

So creating all these funky financials is great, but if you are using those in a presentation that information should be in the PPM or an official document as if someone is making a decision based on that - it can come back to bite them.

I have a choice to ask the seller to pay for my buyer agent's commission or not include it in the offer letter (pay by myself), so I wanted to know before I submit the offer. 

Proper documentation and consistent reporting are crucial to ensure compliance with IRS requirements.

Document all of what you do if you are going to get it done for them, and/or if you cut them a check then make sure it is in writing that it was all done and they cannot come back to you at a later date asking for more money/mitigation.  

An example, a small down payment initially, but the note has now seasoned for 60 months with on time payments documented by a third party servicer.

Definitely not doing the work myself so it sounds like resale value won't be impacted if I have a licensed person fix the issue and provide evidence/documentation that it was done correctly.

An architect can assist you in the initial work to get this submitted to the city for review and approval, and then a GC can pull the permit and work with you and the local inspectors to get this up to code.

But I was also sent a document stating that a county housing assistance program was guaranteeing the tenants security deposit (which was accepted by the current landlord) but not for the full lease term because the tenant is no longer receiving assistance and that the guarantee would only be until 2/2025.