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

Go to Etsy and search for "rental property tracker," and you will find hundreds of nice spreadsheets to track 10-20 rentals, usually for under $10.Software has extremely helpful features like online payments, marketing syndication (click a button, and your property is advertised on multiple sites), electronic document review/signing, maintenance tracking, and owner reports.

I've considered a short sale, but am under contract, I think, with a buyer already due to the commitment to sell document I signed...

A good vendor will often provide insights and a documented professional opinion, which can serve as third-party confirmation.

@Philip Jones we've helped our clients do over a hundred.As some of the lenders posting have pointed out, the challenges are:1) Property value and corresponding loan size2) Appraisals have much better comparables than 5 years ago, but may still be an issue.3) Property condition can be an issue via the appraisal4) Ownership seasoning - most lenders looking for 6+ months or incredible documentation for cost of improvements made.5) Most DSR lenders require professional property management.Always try a small local bank or credit union, but most will expect you to transfer your business bank accounts over to them. 

Short term, assuming the real estate lobby doesn't sue this to keep delaying/appealing, once it goes into effect there will be no more broker fees paid by tenant *unless they hire the broker*Some long term effects I can predict already: - Landlords now having to absorb broker fees will bake this into the rent (e.g. how "no fee" units typically are priced a little higher than other units) - Real estate board will require another document (or checkbox) for tenants to sign stating that they're hiring the listing broker and responsible for compensating them for their fee *if* they apply and are approved- Regular New Yorkers will have an even harder time to find an apartment because you cannot legislate/regulate away a housing crises... 

That being said, here’s what I would recommend for a thorough DD process:-Build a plan in advance (setup a spreadsheet, meet with the team, etc)-be prepared to take a lot of pictures -document notes with each room (we use notes on Apple and share it with the team)-align the team on standardizing information (example: what does “bad” mean, what does “okay” mean, etc - everyone looks at things differently and you want to make sure the notes are accurate during your debrief)-bring in professionals for things you can see, like sewer lines hope this short list helps! 

@Yixin Huang when it comes to accessing the property and maintenance, you want to DOCUMENT EVERYTHING!

Those that respond “$0” or something ridiculous, you can request income documentation from them to justify.Don’t be afraid to share with them how much your property taxes & Insurance increased and that YOU cannot afford to absorb them.ALWAYS get an increase or something of value annually when rents are increasing or tenants will start thinking they should never have an increase, making future increases that much more difficult to negotiate.

However, professional remediation is essential for quality results, complete documentation, and assurance that the job meets industry standards.