I have commissioned several artists in the past, but I've always been a bit disappointed with how fragile the paint ends up being. As far as I know they used primer and water based acrylics. I can scratch the paint off gently with a fingernail.

Sadly I can't paint with automotive laquers myself, due to health concerns, but I am thinking of commissioning an artist to do it for me. Would an automotive laquer hold up better?

Thanks  

 

Lacquer will always be more durable than acrylic. It generally goes: Lacquer, enamel, acrylic in order of durability. It's due to the difference in how they work. Acrylic is a surface coating, laid on top of the surface you are painting. You need to give it a long cure time and top coat it with another long cure and it will still scratch comparatively easily. Lacquer paints work by ever so slightly dissolving the surface of the plastic and mixing in with the plastic before solidifying so when it dries, the paint is impregnated into the plastic. Can still scratch of course but it's much tougher. The down side as you noted is that the fumes are a lot more toxic, you need powerful thinners to clean up and the colour range isn't as easy to acquire. There's a wide range of colours available in auto lacquers but you need to buy a touch up spray can and decant the contents, then load into an airbrush, if you want to do it properly. A can of auto lacquer costs a fair bit more than a tiny jar of Tamiya or Valejo acrylic, though you do get a lot more for your money.
Personally I use an auto lacquer-based primer designed for bumpers and plastic parts as a base coat primer on all my models. You get a good strong base coat that resists scratching and then you can paint with normal model acrylics on top. It's not as good as painting purely lacquer based paints but I find it a decent compromise. I still get paint scratching issues though.
Here's a great article on the specifics from the same guy who wrote the definitive article on Future as a top coat:
The Secret Life of Alclad II