Why then do they pay $35,000 to obtain what’s basically a sales position?  

I'm totally good with some sweat equity but I'm not in a position to do Roof, siding, structural repairs and such.

Luckily, my wife and would be in a position to buy their house from them at fair market value, if that is the best option? 

I recommend before spending thousands of dollars on this you speak to your CPA and your attorney as they will understand your overall financial position and the risk.The question I love to ask is "what are you afraid of being sued for that insurance would not cover you on?"

@Melissa Sejour  The search function shows many have used itReviews are positive   examplehttps://www.biggerpockets.com/forums/49/topics/310282-busine...

Key Factors for a Good Seller-Financed DealCash Flow: Rental income should exceed monthly payments (PITI) by at least 1.25–1.5x.Purchase Price: Compare to ARV and market value for fair pricing and equity potential.Interest Rate: Aim for competitive rates; higher rates must still allow positive cash flow.Amortization/Balloon Terms: Favor longer amortization and align balloon payments with your exit strategy.Down Payment: Lower upfront costs reduce risk but should meet the seller's expectations.Flexibility: Seek no prepayment penalties and fair late-payment clauses.Property Condition: Ensure the property’s condition matches terms through inspections.Seller Motivation: Assess the seller’s willingness to negotiate favorable terms.Exit Strategy: Have a clear plan for refinancing or payoff at term end.Portfolio Fit: Ensure the deal aligns with your financial goals and risk tolerance.Vetting multiple deals and consulting professionals is crucial to making sound decisions.

If one tenant moves out, the property remains cash-flow positive. 

Here’s my honest advise; consider studying for and obtaining your real estate sales license, and obtain a part time position with a real estate agency that will provide training, guidance, and oversight.  

that we’ve learned in our 24 years, managing almost 700 doors across the Metro Detroit area, including almost 100 S8 leases:Class A Properties:Cashflow vs Appreciation: Typically, 3-5 years for positive cashflow, but you get highest relative rent & value appreciation.Vacancy Est: Historically 10%, 5% the more recent norm.Tenant Pool: Majority will have FICO scores of 680+ (roughly 5% probability of default), zero evictions in last 7 years.Class B Properties:Cashflow vs Appreciation: Typically, decent amount of relative rent & value appreciation.Vacancy Est: Historically 10%, 5% should be applied only if proper research done to support.Tenant Pool: Majority will have FICO scores of 620-680 (around 10% probability of default), some blemishes, but should have no evictions in last 5 yearsClass C Properties:Cashflow vs Appreciation: Typically, high cashflow and at the lower end of relative rent & value appreciation.

But if your goal is to cashflow positive from the Day 1, you may find it very challenging due to current day interest rates, high cost of construction and the fact you won't have the efficiencies of a seasoned developer building at scale.