You have to attract interested parties that are willing to sell you their property cheaply because they need to vacate ownership for one reason or another.

Your QI will own the property you are buying and you have to have bought the property before you sell the downleg.

Sell the property, buy cheaper, and have more cash to put into another?

It's the complete opposite where I am - no one will sell their existing homes because they won't give up their ultra-low rates.

He can sell you a worthless education and there is no consequence. 

When selling a primary residence you have lived in 2 of the previous 5 years you get a tax exception on profits of $250k for a single person and $500k for a married couple filing jointly.

Can I just sell it off to a collection agency.

Quote from @James Wise: The term "cross selling" is used when you sell related products.

One day he calls me and says he and his wife want to sell a building they own and they thought of me. 

Most lenders sell their loans out.Nobody wants a loan where the asset is underwater every month.The real question is, why is a property worth over $1M only producing $4,000/mo.You should consider raising rents as this seems significantly below market.