Again, intent is important. If you're going to the store to touch, feel, try on, and get info about a specific piece of gear knowing full well that you have no intention of buying it there, but giving the sales person the idea that you may buy one, then I think you've abused the store.

In your example, you really didn't know what you were doing; you stop in and the clerk says, "May I help you?" You say, "I'm looking for a pack, mostly just browsing, and don't really know what I want. I'm not going to buy one today; I want to shop around and check out some other brands." Now the clerk has a choice: spend his time with the other customers who are buying, or spend time with you hoping to develop a new (hopefully loyal) customer. But at least he knows what game he's playing. We've all done that.

Then, if you find it somewhere else, I don't think you're obliged to go back to the first store.

Ethics is what you do when no one is watching.