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That “write your own mortgage” thing; how to learn about it
If an entity or individual has full rights to the land and land improvements, they can hold, transfer, delegate, or dispose of them on their terms.  The only exception may be eminent domain.  If the sovereignty meets the public necessity or public purpose tests they can assume or change the rights to your property in exchange for compensation. As others have said writing your own mortgage falls under the category of seller financing.  A seller can write a mortgage with the help of a loan servicing company.  Some loan service companies report to credit agencies, to help with buyer refinancing at a later point. Other forms of seller financing: Leasing Land contracts mineral contracts  and more... Additionally, the seller can finance the minority of the property, called a junior mortgage.  For example, the Bank finances 79% of the value, the seller finances 11%, and the buyer's 10% down payment covers the rest.  If the buyer defaults, the superior mortgage (bank's) has collection priority. More commonly, the seller can option for a wrap-around mortgage or an 'all-inclusive mortgage'.  The seller holds or refinances the existing mortgage  and provides a junior mortgage in exchange for a secured promissory note and an all-inclusive trust deed.  If the buyer defaults, the seller has foreclosure rights. It is not uncommon for entities or people to use financing strategies other than the traditional mortgage if they are unable to exclude the gain on sale.  Check out section 1031 exchanges.  In almost all cases I would tell people not to make decisions based on tax consequences alone, if your financial objective/goal for seller financing sounds like a 1031 exchange, take exception and carefully consider the tax consequences.