Transaction on the blockchain require a balance of ZIL in order to be submitted. You have to pay a transaction fee to the network everytime you submit a transaction.
The current required balances are:
Creating a store: 60 ZIL ( 40 ZIL is refunded )
Approving an item to be sold: 40 ZIL (20 ZIL is refunded)
Listing an item for sale: 50 ZIL (25 ZIL refunded)
You need to have the USD amount listed for the item's price, in your wallet. So if its going for $10, that would be roughly 200 ZIL needed in your wallet. The ZIL price is listed when buying the item.