Milton Friedman brilliantly described the four ways that money is spent.
The first and most common way in the private sector is people spending their own money on themselves. In this case, the buyer is interested in both quality (the best product or service that he can afford) and value (getting it at the best price) because he is both the producer of the wealth being spent and the consumer of the good or service being procured.
The second way is when people spend their own money on others (such as gifts). Here they are still concerned about value (it's their money), but less concerned about service quality as they are not the consumer.
The third way is spending other people's money on yourself. Think of the rich man's girlfriend who buys herself the nicest dresses in the store on his credit card without even looking at the tag. She wants quality, but value is irrelevant since she sacrifices nothing.
The fourth way is when people spend other people's money on other people. In this case, the buyer has no rational interest in either value or quality. Government always and necessarily spends money in this fourth way. This guarantees inefficient public spending because the spenders have no vested interest in efficiently allocating those funds.
I have seen this firsthand working in government myself the past few months. The way people talk about spending huge sums of taxpayer dollars on a whim was shocking to me at first. The shock is wearing off a bit by now. One must become desensitized after awhile. Good thing I'm only going to be here a couple more months. People in government will argue that they have the "public good" in mind when spending this money, and that itself will be enough of an incentive to spend it just as wisely as they would for themselves. I don't believe this for a minute. One thing is the desensitazing issue I just talked about. I just can't be convinced that year after year, decision after decision, someone is going to hold themselves to a standard of spending large sums of money for both value and quality when the only thing to guide them is the "public good".