Have you ever sold your property "over time"?

Have you ever sold your property "over time"?

Bear with me, i'm trying to actually think here. Stand back, this might get messy.

So I have this "buyer" with good credit, ok income, but his expenses to income ratio, only affords him potential loan amounts less than the total cost of a rental property I'm advising him to get. (no i'm not acting as his lawyer, but as a friend)

Have you ever sold a PORTION of an interest in a property, then waited till the 2nd party builds up more cash and then sold them the rest? Is that even possible? Am I crazy?