(MONEY Magazine) – Maybe I was just naive.

When Amazon admitted last month that it had been testing a form of dynamic pricing, I was--how else to put it?--deeply hurt.

What did I expect? Loosely defined as the practice of charging different customers different prices for the very same thing, dynamic pricing goes on in almost every industry. All businesses try to charge each customer as much as that customer is willing to pay. Retailers have generally had more trouble with this than businesses that sell to other businesses--Americans tend to demand a level playing field when it comes to the necessities of everyday life--but everyone knows airlines and car dealers routinely charge different prices for the same thing.

So what am I so upset about? Well, I guess I'd always felt that Amazon's position at the forefront of e-commerce gave it a responsibility to use the Internet in consumers' interests, not against them.

And Amazon seemed to agree. No, it didn't make any promises, exactly, but it did make certain...representations. "We intend to build the world's most customer-centric company," CEO Jeff Bezos wrote in one annual report. Amazon would "obsess over customers," he pledged. And this: "We hold as axiomatic that customers are perceptive and smart."

And what can I say? I believed it! After all, every paperback was 20% off; every hardcover, 30% off. Amazon even took the mighty New York Times to court so that it could, as a press release put it, "continue advertising and selling New York Times Best Sellers at 50% off list price." Amazon did it all for us!

Then came the betrayal. A University of Michigan professor noticed that a particular DVD was selling for between $80 and $100, depending on what computer you were shopping from. Amazon later claimed that prices had been arbitrarily assigned to buyers, but it appeared to many that the company was toying with the idea of charging regular customers more than new ones. It looked, in other words, as if Amazon was taking its best customers for granted.

Yes, I know companies will be companies. Yes, I know that even Amazon boosters like Internet uber-analyst Henry Blodget have been demanding proof of Amazon's profit-making potential. And yes, I know that Amazon apologized, promised to stop the "test" and refunded the difference to those who paid more than others.

But in my mind the damage is done. Amazon is just another company out to make a buck--and I, as a consumer, am its reluctant enemy.

--SCOTT MEDINTZ