I've tried the carpet powder, vacuuming that up, and even using my portable carpet steamer for the floors and Lexol for the leather seats. Still there's remnants of the previous owner in the car. I do still need to condition the seats. Think I'll try steam with the portable again plus try something that neutralizes odors rather than mask /cover them.

You might try a Lysol-boil like we do for cars with mold which has crept into the upholstery and headliner. Fill a common kitchen crock pot with 50-50 water and Lysol floor cleaner (Pine Sol works just as well if you prefer), place it on the back floor and run it on medium overnight with no lid on the pot and the car closed up. Tilt the rear seats if possible to let the fumes reach the trunk as well as the cabin. The windows will be completely fogged in the morning and the Amazon rain forest will hit you in the face when you open the door, but the Lysol will reach every hidden corner and surface in the interior.