According to a new study by the University of Pennsylvania (a telephone surevey of 1,500 adults), 87% of people strongly objected to online stores charging different prices to different people.

Of course, this is a common practice. At the low end, sites test different prices all the time. Indeed, if you’re not testing, you’re not marketing.

At the high end, sophisticated e-commerce companies are able to offeer different prices to different visitors based on behavior. For example, a site visitor who was referred by a shopping engine may be offered a better price than a normal visitor.

Also, as companies seek to retain loyal shoppers they may offer better prices to site loyalists than people just seeking the lowest price for a one time purchase.

As a practical matter, though, merchants should keep in mind the lifetime value of the customer. Earning less profit on the first sale may be all right if the customer has a good experience and returns again and again.

At the same time, as consumers, it’s good for us to be aware of what’s going on. In this recent Pennsylvania study, called “Open to Exploitation,” more than two-thirds of participants thought that online travel sites were required by law to offer the lowest airfare possible. Argh.