There's a reason that people try to buy properties off-market and that is because you can find sellers who care more about terms than maximizing returns.So start with a conversation: you already presumably have some rapport since it's your landlord and you've spoken before.

Quote from @Blake Steagall: Hello @Jaycee Greene, I do not own any real estate in that market yet but am interested.  

It requires no money upfront, so you will join thousands of others trying to do the same in your market.

With a HELOC being around 9% I'd probably be paying more in interest than the money would make in the stock market.

Over the years the only place I have lost money is the stock market.

Look at their marketing strategy.

Most times when evaluating a DSCR mortgage, market rent will come into play.

Make sure to factor in insurance (slight change as rental), property tax (in our market is 2x a primary res), vacancy (3-5% in most markets), capex (old roof?)

Few agents in the market understand seller finance and the many ways it can be structured, and few will sometimes promote it, but the rest are just risk averse.

The reality in this market is that you would likely not have any funds left to return to them since it is unlikely to get re-rented so soon.