I am actually scheduled to double close on a mf deal in a couple of weeks.
Assuming the deal will leave you a juicy 5 figure fee or more, you will probably have to double close unless the buyer is paying cash. The banks will typically have a huge heartburn about a fee like that and will not accept a regular contract with an assignment like you see in SFH. Another option is to amend the contract to the new purchase amount with your fee included, with the new buyer's name and assign it after. Both the assignment and the addendum get sent to title at the same time.
Just make sure both parties and the title company are ok and aware of the double closing and you should be fine. Sometimes you will need to come up with the money to close, sometimes you wont, depends on the deal and title.
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