Practical chart, DamonHD...
Gives one an idea of the state at a glance...
My experience with sealed lead-acid batteries are that fully charged, they have a 'at rest' voltage at around 13.00v when they're healthy.
When buying a new one in a shop, it would depend on how long the battery has been stored in the shop without any charging. According to the spec. sheet for one of mine 12v, 7.2Ah, the selfdischarge are at 92% after 1 month, 90% after 3 month, and 80% after 6 month. (All at 20deg. C.)