Farmer's daughter joke

Seems that the traveling salesman was driving in the country and his car
broke down. He hiked several miles to a farm house, and asked the farmer
if there was a place he could stay over night.
"Sure," said the farmer, "my wife died several years ago, and my two
daughters are 21 and 23 but they're off to college, and I'm all by my
self, so I have lots of room to put you up."
Hearing this, the salesman turned around and started walking back towards
the highway, and the farmer called after him...."Didn't you hear what I
said? I have lots of room."
"I heard you," said the salesman,"but I think I'm in the wrong joke."