Well, assuming you mean 'dumpy' but not quite '****hole'...
Smell, there's got to be a bad smell, a combination of old beer, BO, and the hint of rotten stew.
There's not a real floor. It's probably straw over dirt.
Most of the place is in disrepair, holes in the walls, drips from the celing, creaky doors.
As long as it's not troubling the inkeeper or causing damage, violence and theft is ok.
The food's just a bit funky. There's this taste that doesn't quite fit.
The cups are chipped, badly finished and mismatched.
Chairs are a hodgepoge of bits and pieces of unfinished wooden stools, rags as padding, and logs cut to size.
Despite that, there's a fire to keep the place warm. Unfortunately, the chimney doesn't work exactly right, and the seats nearest the fire are a little smokey.
And, of course, the tables wobble.