Personally, I've never seen P. lunulata in the flesh, and to be honest, unless your LFS and the wholesaler are really up on lionfish ID, I'd be surprised if the fish is correctly ID'd, as it is rare in the hobby. I'm not knocking your LFS, however, I've seen WAY to many lions mis-ID'd at LFS as well as wholesalers to believe it without seeing the fish myself.
The luna lionfish is very similar to P. volitans, however, the fish reaches a slightly smaller adult size, has partially-webbed pectoral rays (about 2/3 the length of the rays), have more rounded heads which may lack many of the dermal flaps that P. volitans has, and the dark stripes have a net-like appearance owing to a white "spot" in the central part of their scales. Also, the median fins are almost clear, but do have a few spots on them.
Care is the same as for any of the large-bodied Pterois species.
It's a great score if the fish is indeed P. lunulata...
I'd love to see some photos!