Asbestos is a killer - but it takes years to do it........ goes into your lungs and stays there - read up on it if you want to know more..... Not nice really...
It is more dangerours in its raw state - like a lot of cotton wool - it was used as an insulant and fire retardant.
It is more dangerous if you cut it or drill into it and create a lot of dust....... There are a lot of specialist Asbestos Companies about who will assess and then safely remove asbestos (and products with Asbestos in them), search for an organisation called ARCA...... this is the Asbestos Association
Now adays, most of the worst stuff is known about and has been removed or is being manage; but Whitebeam is right, asbestos was added to Artex pre early 80's. But there is not that much in it......
If you think there is some in it, best to get the client to get it looked at....... or get some specialist wet artex remover and soften it first and keep it wet as you take it down.....
OK - previous job, I used to sell specialist products into the Asbestos Removal / Abatement industry.........
If you don't like it and don't know - get the client to find out and sort it before you plaster or skim it!
That said - It is your living and life.......
