It wasn't that 20k was unheard of, in fact, it was not uncommon.

So I’m really curious if it’s unheard of that the seller would fix what’s needed if it’s as severe as that

Just diversify your portfolio a bit.Then youd be able to live off the cashflow from your 3 other 4plexs, since you have no living expenses, yes you wouldnt be rich or anyhting but you could live a comfortable frugal life without having to work.This way you'd have money thats fairly liquid as well in your TFSA, in case you had to do any repairs or to account for miscellaneous problems that could occur, and in the very worst case you could do a HELOC  to pay for any major major disaters that could occur with all the equity youve created in your home by using the BRRRR investment strategy.These numbers are just examples, however its not unheard of to BRRRR a property and actually come out with more cash than it cost for the DP and Renos, which would help acquire even more property.And if you can get 50K into your TFSA and get a return of 8% from a dividend then thats an additional $350/month roughly, all while living for free. 

It is possible/feasible or unheard of to request that the previous owners file an insurance claim as the damage occurred before I moved in?

Jonny Morris Unheard of...If he was running it to the main sewer connection sometimes the town/city has to do that.

Prepayment is a little odd, but not unheard off.

@Sean McDonnell , $10 cleaning fee is unheard of in STR.

That’s unheard of now!

Air has become a hot commodity in cities such as New York where developers are prepared to pay sky-high prices to add more square feet to their projects through the purchase of air rights.In fact, in a crowded city where the only place left to build is up, air rights are now fetching 80% of land values--previously unheard of pricing--according to top Grubb & Ellis appraiser, Robert Von Ancken."

Unheard of for most mutual funds.