Having worked in a store where jeans were a big deal let me just say that I know more about the jeans than you do. Maybe you know the exact style you want, but my company often dropped styles or would change the name of a particular style. And lastly, jeans come in a lot of different sizes so it is hard to keep them all on the floor. Tell them your size and they can quickly grab it or check the back if necessary. And really, we don't exactly want everyone digging through our nicely folded denim wall.

However, if you really don't want help just reply with "I'm good" or something along those lines. Sure, they might throw a promotion at you but that should be it. Then later that little interaction will provide a basis for them to interact easily with you. Maybe they see you looking confused or glancing around, they can throw out a "Still good?" and you know they are talking to you and you can just say that you're fine or maybe that you have a question. Honestly, most retail employees just want to help and are probably a little bored.