Anyone can walk into a beauty supply store and get Bigen Black Hair Dye.  It's cheap.  You just mix it with water and use it.  Or, you order it off the internet, and that seller is handing you black hair dye, repackaged and perhaps remixed as "Black Henna".  It's easy to stain your skin black quickly with black hair dye.  It's also illegal and dangerous! 
 

2) Profits on PPD sold as "black henna" are unbelievable.

A package of Bigen Black Hair dye costs less than $10.  A street artist can use that package to make $1000 easily in a day.  With that kind of easy money, do you think they care that they're hurting people? 
 

3) Henna takes patience and care to learn to use

Henna is an art and science and takes time and patience to learn to do beautifully.  However, ALL the information you need to do safe, beautiful henna is on this website, The Secret Henna Diaries, TapDancing Lizard, and The Henna Page Forum. 
See: http://reverndbunny.sphosting.com/reverndbunny_sphosting_com.html
http://www.mehandi.com
http://www.hennapage.com/
 

4)  PPD "Black Henna" looks like a tattoo ... until the blisters and festering sores come up.

People want something that looks like a tattoo. At first, PPD "black henna" may look like a tattoo.  Later, there may be itching, blisters, open sores and scarring. 
 

5) Do you want to find an artist who does safe traditional henna?

Look at the listings on http://www.hennapage.com/henna/where/artists.html . Those artists have guaranteed that they ONLY do safe traditional henna! 

Do you want a source of safe, pure henna?  See the suppliers listings at http://www.hennapage.com/henna/where/suppliers.html
Those suppliers have guaranteed that they will ONLY sell safe, pure, traditional henna products and have all the ingredients listed on their sites.