I am an experienced investor and unexpectely find myself managing a duplex myself and wondering if there is a small landlord (aka inexpensive) simple solution for marketing, background checks and lease creation that markets on zillow? 

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How to Structure the Deal to Protect Your $20KIf you’re willing to cover the $20K arrears, here’s how to protect yourself:Option 1: Secure Your Funds with a Lien or Escrow AgreementUse an escrow account: Deposit the $20K into escrow with clear terms—if the assumption is denied, the funds return to you.Record a promissory note & lien: If the deal falls through, this would give you a legal claim against the property to recover your funds.Option 2: Sub-To + Wrap While You AssumeSubject-to deal: Take over the existing loan payments before assumption approval, securing control.Escrowed deed transfer: The seller signs the deed into escrow only to be recorded after assumption approval, ensuring they can’t back out.Lease option fallback: If the assumption is denied, consider a lease option agreement until another solution is found.Option 3: Negotiate a Seller Financing HybridAsk the seller to carry a small second note for the $60K equity gap at favorable terms.Use your $20K as a down payment, structured as a secured loan against the property.3.

It's a learning curve, but I think it's going to be the best solution. 

I like fitness and health and just like those two things, real estate investing is NOT a "one size fits all" solution.  

Old lists which are on the mentioned platforms practically guarantees saturation and others already having reached out and made offers/solutions because all your competitors are getting the same leads and at the same time.

I don't have a good solution for smaller properties, but would be interested in that solution as well.

I am not exactly sure if calculations are accurate and feel stuck with this decision, I would appreciate if someone could offer an advice or potential solution?

As others have noted, it's not perfect (no software solution will be), but It does get the job done.

I think I have a solution in mind but since this would be my first deal I may be missing something important.