Double check that ice-maker (make sure no ice blockage, and no water leaking out of the rear of the fridge). 

If you overload a septic with a large amount of water you could get a backup but a blockage or problem with the line is also possible.

The plumber tried to use his snake to clear the blockage from the vent right outside the front of the house.

There are times that I forgive the bill but not before i hand it to them and make them aware of the cost.Lately been dealing with a lot of drainage issues and now updating my leases to inform tenants if they are the cause of blockage expect a bill from me.One of my pet peeves is the water bill.

If you can prove that the blockage is caused by the tenant not by defective plumbing system, you can ask the tenant to pay for it.

The blockage was far down the line.

If the toilet was overflowing the blockage is inside the pathway of the toilet, because if it's further down in the pipe more than likely your tub or shower would be backing up before the toilet bowl overflows. 

The biggest factor was that trades, in general, tend to be quasi accurate in their estimates, less punctual, less reliable, less professional and have themselves overbooked which resulted in more blockages in the project timeline.  

When hiring an inspector ask if they run a camera down the main line to check for cracks and blockage?

(I had something similar happen altho it was guys not reporting a small toilet blockage that ended up costing me 25k - luckily my insurance covered it all.)