Typically means it's not the page they're looking for.
You should be looking to increase the focus of your pages. Some pages will contain general content and you cannot do much about it other than restricting spider access (eg: privacy, tos etc). But the pages that are important for sales should be tuned to expose specific information about the items you sell.
So if the visitor searches for red widgets and ends up on your site because you have some generalized widgets, he will likely leave right away.
You should also check details of the exit pages because the bounce analytics show, is a general graph at the top and you need to see each page's details underneath. What's the bounce of the checkout page or shopping cart page for instance?
And yes if someone hits back on his browser that's the exit point.
Also there are no reliable bounce figures for ecommmerce stores assuming you have the right page focus, because the merchandise and/or type of store, changes pretty much everything. Could be 10% or 50% or 90%. What type of products you carry? is it a niche? something custom? or something way too common. But the pages that you rely on to make sales is what you should be looking for to improve. Check those for the bounce rate.