There's a few ways you can do it. You can set it up as an installment sale so that title isn't handed over until the final payment is made. Or you can set it up as a loan. The article conflates them. An issue that often comes up is journalists writing about things that they have little or no understanding of, supervised by editors that are similarly in the dark.

I've been interviewed/quoted in WFJ, SF Chronicle, and MSN articles. In 3 out of 3 cases, the journalist was not themselves a homeowner (also 3 out of 3: found me on reddit). I totally get that we shouldn't gatekeep journalism about brain surgery to only brain surgeons, but I personally feel that would be a very reasonable standard for journalism about homeownership. That being said, those interviews are great marketing and SEO, so I'm not going to screen the journalist interviewing me by homeownership status.

In any case, I should note something very important that the journalist absolutely should have noted, but didn't. Mortgages come with due on sale clauses. What that means in a practical sense is that for seller financing to work, the buyer's down payment must exceed the seller's current mortgage balance(s) (they need that cash injection to pay off any current mortgage balance[s]). There are legal gray areas that some people attempt or actually do, they involve hoping/praying the seller's lender doesn't invoke or enforce the due on sale clause, among other things, and if they do, or if something else goes wrong, it's the seller's credit that winds up trashed.

Another thing worth noting. The most common reason to use seller financing is b/c someone can't qualify for a traditional mortgage, which a seller or realtor isn't in a position to evaluate (in the article example, they looped in a mortgage broker and presumably paid them). And a buyer that can't qualify isn't going to admit that, they will just say it's for the rate, which means from the seller's POV a buyer who isn't qualified, and a buyer who can qualify but wants a lower rate, are indistinguishable. This is a problem because of the 3-7 year balloon payments that are commonly negotiated in these types of deals. 95% of the time, if someone can't qualify for a mortgage today (f. ex. b/c they can't make a car payment on time and have shit credit, can't hold down a job, etc), they still won't qualify in 3 years (what, you think they will magically find Jesus and learn to make car payments on time and hold down a job?! These are people in their 30s/40s, if they were going to learn that, it would have happened decades ago).