http://businessinsavannah.com/bis/2014-08-30/bitcoins-what-you-need-know-about-cryptocurrency#.VAK6FaOrYU8

Speculators who rushed to purchase bitcoin were disappointed, however, as it subsequently lost more than half its value, dropping to its current worth of approximately $588. Clearly, no business with a 3 percent profit margin wants to accept such a volatile form of exchange.

Returns also could present problems for retailers who accept bitcoin. Imagine an item purchased for one-tenth of a bitcoin, which is returned a few weeks later. The customer expects to receive one-tenth of a bitcoin in return for the item, but the value of one bitcoin has risen from $500 to $700 in the meantime.