If you had showing and no signings, I may ask about interior issues like smells or stained carpet.....If you got interest but no filled out applications, I may ask about the terms, policies, processes, fees and more....I like the idea of finding out first if you are getting prompt responses to inquiries. 

The original floor is Red Oak and I did my repairs with White Oak so I stained the floor Espresso to turn those blotches into what we call "historical character" - LOL. 

so here's the next "issue" in front of us:We just closed on a very old house and inside there is gobs of original wood:  exposed ceiling beams, (tons of) paneling, rather wide door trim, doors, etc. and it is all stained very, very dark brown.  

I can definitely paint the stain, but when the water are coming into the porch again, he will experience the same observation. 

You need to be very careful to properly sand the floors and take out all sanding marks, and you will need to be very careful when applying the stain/sealer so as not have puddles.

now, what if they had stains on the floor and paint?

-make sure doors and windows open and close properly if some of them don't could indicate structural problems-check ceilings for water stains or stains that might be covered up with paint, or rough spots on walls could indicate water damage or possibly mold-ask seller to purchase a home warranty in your offer just in case heater or central air takes a dump-make sure floors are level, if not check beams, or foundation outside for cracks these are some major things to look for, but not deal breakers at least for me. these can get you big discounts and can be fixed

Also, FYI, some of the concrete structures that look stained or dingy by age...Check into Soda blasting.

If I'm buying a 1979 ranch, I'm not so sure I want to see the grungy bathroom and stained ceiling before photos - or even told how bad it was.I understand from the rehabber side that you're proud of the work and it's cool to show off how bad something was before and how great it looks now, but should a buyer be told how bad it was?

Interiors vary from pretty worn (stained carpet, dated/mismatched appliances, etc...) to good condition (newer finishes, but not NEW).