These days?
Could be connected to totally abandoned, yet paid, accounts. Over the last 6 years, so many vets have quit and yet some still have houses connected to accounts in good standing.
Frankly, it seams pointless to me to print "FOR SALE" on a plot and have zero contact information. No storage of people looking to sell, active, in game... connected to the actual game. I've seen a lot of small places fall with stuff inside where I saw people just the week before. This on Atlantic? Its crazytown. hehe
Also... I've been seeing runes for places "for sale" now and then, dropped around. Just have to keep an eye open. Warning: Prices are looney now a days. Heads up.