I'm a landlord of a duplex and a couple weeks ago we heard a loud argument (we live on the other side) and then she left with a suitcase and we haven't seen or heard from her.

Can't fit a ladder in a suitcase (although some tools, paint supplies, etc., travel well).

As to the suitcase, this is where I store client files.

Seller - Gives you all the info.Antonio - What is the lowest price you will sell this house for today.Seller - Gives you a number.Antonio - If I were to come to your house tomorrow morning with a suitcase full of cash is that the best price you could do?

Another said he wanted to be paid in small bills left in 4 suitcases at various locations around DC.

At this point in my journey, living out of suit cases is awesome! 

You are looking for signs of someone visiting (suitcase) or someone living there (closet is full).Next, assuming occupants not on the lease have moved in you will need to decide if you want to address this face-to-face during your inspection or send an email. 

@Blair, any constant flow of strange cars and strange people dragging in suitcases at all hours of the day and night, especially with families, pets, or groups of people will disrupt the tranquility of a neighborhood. 

I make "cash" offers all the time on properties where I'm not planning on literally bringing in a suitcase full of cash.

Although an Airbnb here and there doesn't make much difference, the impact of those 50%+ Airbnb buildings is definitely negative- lockboxes on every railing, suitcases and confused travelers in the lobby, late night parties, cleaners constantly in and out, unauthorized persons entering and exiting the building...You've got a great idea - we own short term rentals in Seattle, Stevens Pass, and Alaska, and our ones in Seattle are EXTREMELY PROFITABLE.