If I know where to find a particular item I like going shopping for it. If I don't know who sells a particular thing then Marketplace is really the only option. I have in fact discovered several places in world through using Marketplace.
I have my favourite places to buy clothes, hair, skins, eyes, boats, jewelry, and so on, and go to them first. Only generally for more specialist items do I use Marketplace. And if I like what I get, I'll keep the LM that comes in the packet, for future reference.