the prices look cheap to me,
the 12v batteries are probably 100 or 150ah each and new would cost 150 to 200 each,
If they were babied you might get 2 to 4 years of use out of them but if they were not treat well??
You would want have them charged well on one day, let them sit overnight and then measure their specific gravity to see if they are worth the price.
my bus thread, http://www.skoolie.net/forums/showthread.php?t=8860&highlight=bubb