I had two people come after who both hated the smell and I gave them full refunds and let them stay there so it didn't kill my ratings I had - it's very much so a business of customer service.

It was a hard fought battle.

Or you can try to figure it out on your own but it will be painful process but at least you will have some battle wounds.

Quite honestly I'm having trouble understanding your desire to battle and disprove this simply because...why?

Just ask the current owner what the story is, and see if it passes the smell test. 

My tenant passed away and was not found for apparently several weeks, so the smell in the house is unpleasant.  

I may smell like Ape but I am Smeksie!!

You can either cancel and they may reduce the fee to try to save the deal or take the hit and leave a foul review so people know of this bad practice 

The apartment definitely needs work - mold/mildew smell in bathroom, old kitchen appliances, old water heater, zero closet space, minor flooding in the basement, etc.

Surely you have some boots on the ground fighting the onsite battles for you right?