IF you have the right eyeware and decent clothes includung a reasonable hat, 2 hammers  makes for quick work at the joints,,,or a sawsall on the pipe BUT hot sparks everywhere.For cracking cast off flush and square Jons tool is top notch. 

Know who is buying: out of town/state buyers flush with cash; investment pools; etc.

I am also scared that somewhere in the slab (although no indication of that) and also in the shower and toilet (again no indication of that, water flushes smoothly to the sceptic and no funny smells outside) the plumbing is bad.

Unless you are flush with cash, it's not the time to be buying investment property. 

Agents today have to do so much more than simply be information gatekeepers.I doubt AI will totally replace agents, but it makes the really good agents have to continue to find more ways of providing value and it flushes out poor and mediocre agents. 

Also, last but not least, should I be concerned with flushing a water heater once a year and having lint traps cleaned by property mangers?

I’m guessing any trees are cleared “near your lot line and tree” they would likely flush cut it and leave the stump/roots in the ground, not affecting your tree.

We paid over $400 to get things replaced & flushed, but still he didn’t have hot water until tech went inside apt & replaced aerators & shower heads.

This is the simplest method, but it also means your tenants are more likely to abuse the utilities by leaving windows open with the heat or A/C running, leaving lights on, ignoring the toilet that constantly flushes on its own, etc.3.

Also change hvac filters and if you have change in seasons you should have hvac servicedYes you can say tenant will do this but when they don’t and your hvac equipment lasts 1/2 time it should etcOther things such as flushing water heater, checking shower valves, faucets etc for leaks, replace caulking etc, checking windows close properly….Myriad of things to do and check.