Pushing disposable cans of refrigerant is highly dangerous to the
general public who knows absolutely nothing about how to properly add
freon to the proper and safe level of their cars a/c system.  If you
look at the specs for your cars a/c , it will tell you precisely how
much refrigerant is required (IE :  1 lb.  5 ounces) ;   this exact
quantity of freon has to be measured in by a Service Technician with the
correct equipment.     You do NOT just 'add a shot'  of freon  to the
system .  Further,  if Joe Public gets a shot of your freon in his/her
eyes with blindness resulting,  would you be willing to compensate him
for his pain and suffering ?