what does "set the store on fire"here mean?
 Hall leaned forward, ignoring Bermond’s deepening frown beside him. “In my opinion, Majesty, you can’t allow the Mort to reach New London a second time.”
“Why?”
“Because you only have one thing to sell, Majesty, and you’re not willing to sell it. You set the store on fire.”
Did the statement convey disapproval? Kelsea couldn’t tell. The feeling was familiar from conversations with Mace. “So what do you suggest?”

Question

what does "set the store on fire"here mean?
	Hall leaned forward, ignoring Bermond’s deepening frown beside him. “In my opinion, Majesty, you can’t allow the Mort to reach New London a second time.” 
“Why?” 
“Because you only have one thing to sell, Majesty, and you’re not willing to sell it. You set the store on fire.” 
Did the statement convey disapproval? Kelsea couldn’t tell. The feeling was familiar from conversations with Mace. “So what do you suggest?”

Answer

I don't think it's a real store. More a metaphor for reducing options as Chris said above.

Answer

"Set the store on fire" is to destroy your resources/options and leave yourself with little to no control in the face of a direct decision or conflict.

If you have any questions please feel free to find me at http://www.italki.com/teacher/1610322, have a great day :) !

Answer

I believe it means, he destroyed the chance to make trades/sell. If there is only one thing to sell, and he's unwilling to sell it, that means he destroyed that one opportunity they had to do trade. Likewise, setting a store on fire would literally destroy the ability to make trades or purchases. This is just a guess. I've never heard that phrase before.

Answer

This is a fantasy novel, so it's very hard to explain it without the entire backstory (but thank you for posting the passage anyway).

At a guess, I'd say "the store" means "the storage facility". I can't tell if this is a suggestion or criticism.

Answer

'You set the store on fire' is referring to the fact that the store has been destroyed by fire. Nothing remains in the store, as everything has been burnt.