We have seen several things happen - they ask the 1st for money to sign off, ask the seller for a promissory note after closing for monies owed, ask for a certain amount to be left at closing for them, let the seller take the note back as a personal loan. These are just a few.
If you do not have an agent or an attorney get one or both. These are very time consuming and both banks will need to be contacted as to their actual procedure. Depending on the banks they can take 2-3 months.