How to clean a hoarder house?

[Tim Shin]

Hi all! This is my first non introductory post. 

I've been visiting properties today and I went into one where the owner mentioned that the person who lived there was a "bit of a hoarder". Well the result was interesting to say the least.

I've never seen anything like it before. Trash was almost a foot deep everywhere, it REEKED of pet urine, rotting food, several full litter boxes, and a dining room literally covered in some sort of... feces... 

I couldn't really get in to estimate repairs and the owner lives out of state and doesn't know what to do with the place. How do I get something like that cleaned? I don't even know where to start!

Thanks!