Whenever high heels walk into my office with the insides padded to the 9’s it’s almost guaranteed, that the shoe isn’t fitting properly. Possible causes:
- Shoe heel height is too steep and you’re sliding forward, losing arch support and contact.
- Shoe is too short and all of your body weight is crashing down onto the ball.
- Shoe is too deep in the toebox and you’re sliding forward
- Sides of shoe are too gappy and you’re not being held secure.
- You have a high arch and the instep of the shoe is below your arch’s instep.
This problem with this shoe was #5. In this case, heel and forefoot padding were insufficient to keep her foot in the shoe.
Dr. Jenny Sanders Shoe Blog 
Your site is a find – thank you!
So about this heel slippage – I’ve heard that shoe repair places are able to sew extra padding into either side of the inside heel of the shoe to prevent slipping and improve the fit of the shoe in the heel. Is this true? And is this something you’d recommend? Not only do I have a pair of shoes that are otherwise fine (I think) except for the heels slipping, but I swear one of my feet is smaller than the other – only slightly but enough that I can always tell with shoes because that foot’s shoe keeps slipping while the other foot’s shoes is fine.