If it's already cured, then have the LFS bag it in a full bag of water so that it remains covered in water during transport home.
Get small bits at a time if you dont wish to cure it yourself, and add it slowly, maybe a 3lb rock this week, and a 4lb rock next week etc. This will minimize the cycle effect *unless the rock is really uncured and the LFS is trying to pass it off as fully cured rock*.
Use your nose, and sniff the rock, if it stinks, it's not fully cured
Personally speaking though, if you already have some serious money invested in livestock in your tank, then theres no point to taking a chance, and you might as well just cure it at home to make sure. But hey, it's up to you.
I went to one LFS that the worker said their rock was fully cured, then I went back a week later to get some more, and the LFS owner said it was not cured at all. So buyer beware.
Goodluck, have patience, and keep in mind before you get your lionfish, that they can be seen as "watching the grass grow", my dwarf is very inactive just kind of hangs around the liverock all day, might swim once or twice during the day, but otherwise definately very much a rock potato.