Hoarder house or just neglected?

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Are there any obvious signs that a home was a cleaned out hoarder house? We are too late to back out, have already begun the flip. Moved in after getting rid of the cat odor. 

Painted, got buzzed on shellac, and installed new flooring. Kitchen coming out next week.

There is a lingering odor that will not go away, not chemical, feline or decomping rodents. The house is liveable but we just cannot place a name to the smell other than old, dry trash. The smell is very dull- noticeable when first walking in and near the back door. We are more concerned about getting used to it and losing on the resale. 

I have my suspicions that it may have been a mild hoarding case (seller had stated mental health for selling, was unoccupied for 18 months although there were Ramen noodles and some other items that had expired years ago in the cabinets.) 

Overall, does it really matter if it was or wasn't? Would there be a different method for the rehab going forward? Send in the Hazmats or handle ourselves?