A great deal will easily sell itself. 

Used houses in the area sell anywhere from $75-125 a square foot.These are long term rentals that I do not plan to sell.I am reading the Rental Property Investing book and implementing the method that focuses on cash flow and that strategy states you need to have $300 cash flow per month, per property.

Property Managers:While realtors are great at buying and selling homes, most aren’t trained in the intricacies of tenant screening.

They might have a contractor they can get in do all the work and get ready to sell!

Would you be able to pay down the HELOC without selling your home?

Question: why would one choose to build an ADU when existing structures sell for less than the cost of development?

If you do have to move because of a job, you would be safest (in my opinion, i am not giving legal advice or financial advice), i would sell that property to ensure that you did not just purchase with the goal of moving out early and taking advantage of lower rates and lower down payments for purchasing your home as a primary residence. 

It is done without prejudice and is simply a parting of the ways (eg tenant wants to move to another place, landlord wants to sell the property). 

All too typical park owner who took all the profit out of the park without reinvesting in the business then wants to sell you the potential he was too cheap to invest in. 

I predict that the guys who are fully leveraged and cash flowing $100 per month will be motivated sellers when the next big correction happens.actually its either them or they walk and its their lenders selling that is what happened in that time period.. and was pronounced in certain markets.for me personally  I don't want to risk  my credit and finances and borrow 75k to make 1200 a year... or even 2400 a year if its a market that has a history of no appreciation and I don't feel there is going to be any significant appreciation.. 2 to 3% a year does not cut it.but I will take 500 a month negative or 10k a month negative if I think there are huge gains at the other end..