Changing tires.

[jaguar6165]

I have read many posts about the plastic bag method and it seems pretty straight foward, but let me ask a dumb question. Why not use a machine? I have a customer who is a very good mechanic and he said the tire machines should work with no problem. I heard you couldnt use a machine but was then told that the main reason shops wont change them because they are too afraid of being liable for a ruining a wheel. So if a shop is good enough and willing to use a machine why not use one?