It will depend on each individual store. Many sell Fiji live rock while some sell real reef rock. I wouldn't recommend real reef rock or any manmade rock because it is not very porous.
I have had a good experience buying dried pukani rock from Marine Depot. It ships free too and you can use NOCALTAX. I was very happy with the pieces they had sent me and you can request the type of pieces by indicating if you want a main large piece, or smaller multiple pieces. You'll have to bathe the dry rock in muriatic acid because they have a lot of dead matter on them.
With live rock, depending on source, you risk pests. I bought a chunk of live rock from one LFS and it had one aptasia, which ended up into hundreds later on. For my next build, I will stick to dry rock.
Pukani is perhaps the most porous and lightweight rock and it is really easy to sculpt with.