The seller is a not only a very well-respected member here, but also a pretty legendary framebuilder in the American bike scene. Between his reputation and the fact that eBay would surely step in on your behalf if the box does not contain the levers advertised, there's pretty much no reason to demand the box be opened.
While these levers aren't particularly valuable or collectible, demanding that the seller open the box does ruin any future possibility of him listing them as NIB/NOS.