The section of law you quoted says that the retailer can't charge a higher price than that on the shelf. So, if someone approaches them willing to buy the item at the advertised price, they could:

a) agree to sell at the advertised price (legal)

b) agree to sell only at a higher price (illegal)

c) refuse to sell

If they choose (c), then they're not in violation of the excerpt you quoted, as they're not 'charging' at all.