I was always a precocious child, and my parents let me shop around stores by myself. I'm not sure if it was at 8 or not, as I cannot fully remember...

However I agree with the OP on this letter. There should be a sign. I have seen them at many stores that mention the fact that children should be supervised. This is not the same logic as no men in the womens bathroom as mentioned below. If you feel your child is capable of managing himself, like in this specific instance, I can see where the parents may be willing to let him do this.

All these are what-ifs about kidnapping and pedophiles. If the kid knows how to protect himself, then it should be no problem. If the child comprehends the dangers of going with someone who they have never met, and knows how to respond by screaming/kicking, etc. if forced, then I think B&N is busy enough that this would be quite the scene and while scary, there would be little to no harm done in such an unlikely instance.

Additionally, the employee's rude conduct involving telling to the parents across the store and not coming over is unjustifiable in my opinion.

Finally, if the OP is not happy with the service or policies of the store, then I agree that she should go to Borders from now on. Speaking with your wallet sends the strongest message.