Because they are morons. Here's some free advice, stop trying to squeeze every penny out of a book.
"Computer says no"There's some profound wisdom in that.
Also by having vouchers, 20% of days, and then you give away vouchers, you are setting an unhealthy precedent. Customers are going to expect vouchers. Example is Dominoes/Pizza hut. Any one that buys a pizza at full price is a sucker. No one wants to be a sucker, so they will even go so far as make up an excuse that they forgot their voucher then pay full price. The pizza companies know this, Everyone uses a voucher. Its factored in. The only benefit for the pizza companies is the marketing they get out of it. No one wants a pizza hut menu delivered in the junk mail twice a week. Its like an excuse to send out these leaflets to remind you to eat pizza.
Boarders are probably giving the vouchers to existing customers because it would be too hard for them to do a letter drop. So you have the marketing taken care of. People then talk about or give away the vouchers, more talk, recommendations.
"Buy from boarders, here's a voucher I'm not going to use."You may also have increased sales because people feel compelled to buy a book. You have a voucher so you got to use it.
But are these small, incremental/questionable benefits worth the stigma of being a 'voucher store'?
Want to sell more Cd's and DVDs? Sell them at the same price as any other music store. You don't have to compete with JB Hifi or Big W etc, but try Sanity or HMV. Just send down some low level employee to write down the price of a bunch of DVDs and do the math. No one in their right mind is going to pay full price for [insert crappy romantic comedy]. What is a full price DVD, at Boarders its $34.95. Someone is getting screwed and its defiantly not me.