To address this, request documentation, update the lease, address rent payment, consult an attorney, and maintain a positive tenant relationship by communicating clearly.

I recommend you do a google search for "real estate seller financing" and educate yourself through some blogs, then have a conversation to see if the two of you can agree on terms that work for everyone.Be sure to use an attorney to draft the documents, not the same one the seller uses.

I currently only have 1 duplex, however I want to set this up right so it will work for any size portfolio.Currently I haveHome folder>multi family/single family/legal documentsInside the multi family I have Name of property-> general property maintenance/first floor/second floor Inside of first floor (the one currently rented)I have, pictures (before and will have after) / lease documents / a spreadsheet with each month, what day rent was paid, if it was late, if late was fee paid?

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.

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

@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...