Restrict product from being purchased

Nick,
I am using your plugin together with User Role Editor, which allows you to manage groups of users. I was able to set up some of the rules for different user groups, however, one thing still doesn’t work for me.
I’d like some products to be restricted from being sold to specific customer groups. For example, I have Product A which only Group A can buy, while Group B and Group C are restricted from purchasing it.
Right now there is no way to set up Max = 0 in your plugin. I can only set up 0.5 as maximum which does the job at the cost of displaying something like “You may only add a maximum of 0.5 iPhone 7 Rose Gold’s to your cart.”
I realize this may not be a documented feature, but by allowing to set both Min and Max parameters to 0 you would solve another problem in an easy way.
Thank you!