This is a question I get a lot, and the answer to this is how severe are your flat feet? Some people have flat feet that are flexible, and they can get into the position that you need to wear a high heel. Other people have flat feet that is more rigid, does not have flexibility, and is pretty much fixed in that flat foot position.
The person with the flexible flat foot will be able to wear the high heel. The height of the high heel may not be as high as someone without a flat foot, and this is due to the structure and the flexibility of that foot. I recommend women with a flexible flat foot try starting with a kitten heel, one to two inches. If they feel comfortable, and they start to build the strength and flexibility in their feet, then they can start teasing the higher heights.
For somebody who has a rigid, or a flat foot that is not flexible, unfortunately, it is not recommended to wear the high heels because the foot cannot get into the posture or the alignment to properly wear the heels.
Another great tip for women who have flat feet and want to wear the high heels is to start strengthening the muscles on the bottom of the foot. I recommend balance training. That's a great way to strengthen the muscles that pull the foot out of that flat foot position.
Also, women who have flat feet, the duration that you wear those heels, I recommend doing a little bit shorter. You will experience foot fatigue and foot pain a little bit sooner than somebody who does not have a flat foot. Remember to bring your flats or an extra pair of shoes so you can step out of the heels.