RM2k3 again (I STILL DON'T KNOW WHAT YOU HAVE RIGHT NOW):

There's an event command called <>Open Shop Window for the store. Page 2 of the event commands. Put whatever items you want to sell in there (it'll be based on the prices you set in the Items tab, so you have to have items set up to sell)

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For conversation in general, you can put as many <>Message event commands as you need, right after the other. Just double-click on an empty <> line and you'll be fine. I THINK there's a limit on event commands in a single event (it's something like 65535 though)

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Tyrannicide:

I'll also say that pages are preferred for conversation changes, since they don't require you to turn off other event switches to see them alone. In this case, that allows "King Assassinated" and "Boss Destroyed" to affect their own events (say, the king sprite not being there and the boss sprite not being there), while making the townspeople say different things depending on the situation. Of course, it's even better (if it's a linear story line) to use variables for story advancement, but that's more of a "squeeze everything into the smallest possible file" thing.