YES YES YES!!!! The girlfriend may be trying to keep a hold on your son by purchasing the expensive gifts. Have your son return the shoes if he accepted them. Do not even consider paying the difference. Where would she get $60 at the age of 14 to buy shoes for her boyfriend in the first place? A simple card and maybe a movie or favorite DVD or CD would have sufficed. Even a teen age friendly t-shirt would have been more appropriate. This may not be a "good" girlfriend for your son if she is manipulative. Simply explain to your son all of your feelings. He may not agree but he will be forced to listen. From the many parents that I come into contact with, it is the teenage girls and not the teenage boys who are more advanced and more forward when it comes to relationships. Keep your eyes and ears open at all times!!!! Have that parent radar out.
Hope this has helped. If you need more advice, just ask!!!