@Ting Lai I have had countless water heaters repaired and replaced over the years.

He literally had likely done over $50k of work for us in the 8 years including multiple slab leaks, multiple sewer swaps, maybe 8 water heater swaps, countless clogged sewers, etc.  

I have seen countless stories of new landlords doing a horrible job screening. 

@Natalie Schanne said it best and I have countless examples of similar experiences. 

Charlie MacPherson has been a huge help including countless others!

Acknowledging the countless time this question has been asked over the years, I'll just add a couple clarifying points I don't see in the near universal recommendation around Schlage Encode locks: 1.

Instead of spending countless hours reading and learning about the intricacies of this strategy and implementing it, I would suggest putting in one extra hour of month of overtime at your job and pay down your mortgage by that amount and achieve the same overall result of shaving 2-3 years off your term.In short, the method CAN work, but not well enough to make it worthwhile.

I have had countless jobs where you get into the box of tile and find the middle one cracked right in half.

You’ve contributed to thousands of threads on countless topics.

There are countless threads on there about exactly that @David Nemrow, many of them in the last month or so so just search initially.