Most of the stores in New Carthage operate in a very similar fashion, although it may not be what you're used to.
In the stores there will be a "display" (display is the default, look for a clue in the description of the room), to look at it simply type:
and to view a specific item in the display type:
look <#ofitem> in <displayname>
Purchasing an item is accomplised by the following: purchase/buy <#ofitem> from <displayname>
It should also be noted that you can shoplift from the store, or even vandalize it...the commands are respectively: shoplift <#ofitem> from <displayname>, and vandalize <displayname>
Be warned that a failed shoplifting attempt, or vandalization...will result in your being blacklisted from the store (the store will activate its security funtion if you enter it), and your being attacked by the shopkeeper