D and E also tripped me up but think a simpler way to go about it is by looking at Net Gains/Losses:

As with the stim, the implication of the cost in D is clear: the loss in customer goodwill exceeds any benefit from theft prevention, hence incurring a net loss.

E says that an electronic keyboard IS more expensive to repair than a piano. But what if the piano costs $3000 more than the keyboard, while the repair for the keyboard is only $1000, whereas the piano repair is $999? E makes no assessment as to whether this potential cost leads to a net negative.