What do people do to ensure the owner gets the letter and it's not thrown out by the tenant living there?

Some one will have the proper bit.

With that being said in most cases for the BRRRR strategy to work properly, you would need to buy a property that needs work in order to force the appreciation to get your initial outlay of cash back.  

If you have proper systems and practices in place and do a reasonable job at tenant screening, the risks can easily be mitigated and there are actually several benefits.

The bank has now put the proper on the market for $265K.

But all the times I went to court and saw other landlords get their evictions denied, the two biggest reasons were 1) not delivering proper notice and 2) accepting partial rent. 

Traditional RE, working with investors, working with new buyers, holding a proper open house.

The fact they are complaining online might be an indication the property manager dealt with them properly so be sure to ask the manager for their side of the story.I hope this basic guide helps.

It's designed to ensure there are no surprises after closing.

He also said to be very careful how the funds (last month and security) are handled during any eviction proceedings, ie be certain to keep funds escrowed properly and not used for legal costs.