I had the repairs done and the buyer did a re-inspection and close the property.

I know that some of the buyers are just people who are not investors, but some are investors. 

I know the seller might need allot of convincing especially in your market to do seller financing now when there might be a more qualified cash buyer that might come along behind you.

The assignment assigns the Mortgage to youThe allonge transfers the note to youAs for due diligence :Are the notes Dodd Frank CompliantHow much are you investing relative to the current unpaid balance (UPB0How much are you investing relative to the current Value of the propertyAre there unpaid taxes on the propertyAre there any unpaid liens on the propertyAre the borrowers currentHave the loans been professionally serviced so you know the pay history and the correct UPBDo the borrowers pay on timehow long have the buyers been in the property, do they pay on timeAre taxes and insurance escrowedIs there insurance naming the lender is there a lenders title policy

Generally speaking, for FSBO, can the buyers and sellers just use the standard MLS form for the applicable state, and simply cross out parts of the contract which deal with agency, etc?

There are contracts in the File section, but as @Laura Alamery suggested, you should probably network with successful wholesalers in your area to get help in a JV deal - You find the deal, they provide the buyer(s).

You can meet wholesalers and get on their buyer lists.

Any prospective buyers?

@Rudy Manna...I believe there are still good deals to be had in MLS but you are more likely to get into a price battle with other investors/buyers acquiring through MLS. 

Does direct mail from buyers / investors work in high income areas, or does everyone in those areas sell through real estate agents?