I do know a bit about cupping as I have worked for a Chinese doctor of traditional medicine (acupuncture, herbs, cupping ect). I have had it done and also watched her do it. I have only had it done in a medical treatment not in play.

I do suggest that if you have never done it before and you are interested that you find a Chinese medicine practitioner and have then do it to you. I know that the Dr. used vasiline on the mouth of the cups so they slid off more easily and were easier to place. Sometimes the Dr will also prick the area to be cupped for extra stimulation to promote a stronger effect. Theres is a surprising amount of suction created by the cups but the marks that are left are not painful, more like a hickey in terms of it looks bad but its not really any big deal. The cupping itself can be very pleasant and relaxing to the person receiving.

I would also suggest that you get the cups from an acupuncture supply place as they are likely to be cheaper than any sold on a bdsm site.

http://www.compassionatedragon.com/cupping.html

http://www.acupuncturetoday.com/abc/cupping.php

I included a few links about cupping from the Chinese medicine point of view as the information about the practice there may be helpful when learning about the practice.