Box breaking, to "own a card shop", is NOT a good idea.
This is strictly my opinion, but I would think you would put out more money doing box breaks and trying to get an inventory together than picking cards up through eBay or buying from others on-line or at card shows.
Box breaks are fun... no, a blast... to do. But if you are doing box breaks strictly for a profit (or in your case to build up the inventory for a card shop) then pass the breaks up.
The profit margin just isn't there anymore for box breaking.
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