That is why they do dumb things like flush yogurt cups down the toilet.  

The plumber who came out recommended flushing the system a couple times a year and we shouldn't have a huge issue but there's only two of us living here currently. 

Many markets are still short on inventory and flush with investors looking to pick up property.

The sump Pump stopped working and made a mess due to something a previous vacation renter flushed down the toilet.

You just flushed that $500 or $1,000 repair “out the window”.

This is a big no no, and people flush these down our toilets more times than I can count.However, since laying out signs in our bathrooms above the toilets stating NO WIPES or anything else besides toilet paper, we haven't had any issues.Regardless, if you do run into issues, getting a plumber out to snake the line can be costly.  

Also they keep breaking the flush lever and I test it each time I replace it, even installed a new toilet for them.

However, I'm sure you can agree, many people got in the game during covid and did good that normally would of failed and the environment of all the lockdowns was what them do well.With things getting closer to normal every day (aside from the inflation and OMG the cost of things because I'm in Qatar and pay sometimes 1/10th of what you do), I feel it's going to be those that succeed are the ones that are putting in the extra effort like yourself and those that were never meant to be in it due to doing poorly or just plain crappy at customer service, they will flush themselves out. 

OOS markets are competitive too, you get lots of competition with cash flush investors from major metros that spent 20 mins googling...

99% sure it's one of the following:Roof leaking into foundation seeping to the bottom of houseDownspout overflow or spillage seeping to bottom of houseSumppump back up or not workingAir compressor leak from HVAC unit if central airClogged sewer line (if toilets are having difficulty flushing)Water forming a reservoire outside due to unsloped ground (need to have a downslope from house to keep water flowing away from foundation)*Next door unit experiencing one of the above