1) Are you incapable of finding the right size shoes yourself? The boxes are usually laid out fairly logically and it's pretty rare for there to actually be anything of use "in the back".
2) Hiring people to provide the level of service you're asking for would significantly increase the cost of labor over the minimum wage kids that usually staff these stores. I'm fairly certain the cost increase would guarantee the store goes out of business with the razor thin margins they usually have. Put another way, do you really think paying 50% more for higher quality employees would guarantee 50% more sales revenue?
A big reason online shopping wins is because no one has the expectation that an actual human will help them purchase things, and the labor and rent costs are tiny in comparison to retail.