I just want to sit back and collect cash flow checks. 

In none of these scenarios are you selling a property that you do not own, you are either selling a property you own (double close), or assigning a contract to collect a fee.

When he sold it was basically a wash, less the cash-flow collected.

When looking back, that isn't an accurate way to do it for a variety of reasons, plus it is a hassle every time to do the math and collect.  

If she pays, then your really out of luck and you have to sue her in court for breaking the lease and damages.In general, I don't take people to court once I have the property back as the attorney fees and the fact you RARELY collect on any judgements (15% of the time or less) eats any profit and wastes your time.

There are many buyers and sellers of sufficient sophistication not to require at least some of the typical bundle of services.

Tenant and Lease ManagementSimplify tenant payment workflows, digitize receipts, and efficiently manage leases, rent collection, and maintenance requests, etc.5.

These factors collectively contribute to a successful sale and maximize the property's value.

Having all my bills go on a credit card and paying them off last day in full. then collecting the bonus points on the card.

And STRs really help because you don't have the large dings that long term rentals have - i.e tenants damaging the property to where you have huge make ready costs (the str insurance covers that), no collections or evictions issues.