Seller financing offered on the first call is a flag I can't ignore until I understand why it's on the table before I asked.

The installment sale angle is the one I'd pull on hardest. Running payment books for land note sellers taught me that the guys who lead with carry and mention no agents in the same breath are almost always working around something on the tax side or the title side, and you usually can't tell which until you ask a very specific question: when did he acquire it and what did he pay. If he bought a six-unit in 2009 for 140k and it's now priced at 480k, the gain is the whole story and the carry terms start making sense. If he bought it four years ago for 410k, the gain motive evaporates and you're probably in one of your first two buckets.

That five percent carry rate is the number I'd push back on. Seller carry on a six-unit around here is coming in at six and a half to seven right now, even from motivated guys who genuinely want the installment income. A seller volunteering five before anyone asked suggests he already ran the math on what he needs net of tax and it still works for him at that rate, which tells you the gain is probably real and probably large.

What does the rent roll look like month by month for the last eighteen months, not just an annualized number?

The framing here is correct, and the installment sale motive is the one most people underweight because it makes the seller look sophisticated rather than distressed. That sophistication cuts both ways: a seller who has done the tax math is also a seller who has done the negotiation math, and he knows that a buyer who understands his motive has leverage on price.

The assumption doing the most work in your read is that these four scenarios are mutually exclusive. They rarely are. The most common version of this deal is installment sale need plus a rent roll he is not eager to discuss, which means scenario three and scenario two are running simultaneously. The tax motive explains why he wants to carry; the rent roll problem explains why he volunteered it before you asked, because getting the carry agreed early anchors the structure before you find what's underneath.

The risk you have not named: the fifteen-year carry at five percent means he is a lienholder for fifteen years. If the rent roll has a problem and the building underperforms, you are in a workout conversation with the same person who sold you a problem. The carry is not just seller financing, it is a fifteen-year relationship with someone whose incentives you have not yet mapped. That relationship needs to be priced into your comfort level with the structure, independent of whether the debt service works on paper.

On due diligence: get the actual leases, estoppel certificates signed by tenants, and twelve months of operating statements before you spend time on offer structure. The appraisal question resolves itself once you see whether the rent roll supports the price. A clean appraisal at 480k on a six-unit requires the income to be there in writing.

A licensed real estate attorney should review the carry note and any subordination terms before you proceed. That is not optional on a 288k private lien.

What specifically did your contact say about the seller's timeline, and has anyone seen the current rent roll?