Just checking. I have the same policy. It offends many DIY's; but I think it is worth it to explain that there is a real reason for codes and professional training; just as there is a real place and applications for tankless water heaters - and it is not just to save money, but to offer real benefits in the quality home and business. High-tech machinery has the handicap of requiring professional attention, so DIY's will have to respect the knowledge that is beyond their reach by hiring professionals that have it - unless they want to take up a new vocation.
I am amazed that homes centers will sell these units, perhaps they don't understand that in time the DIY's will hate them for providing something that takes more than a DIY can handle. Not even a full course on video will supply the knowledge; but a home center would sell that also. Now they'll have to have the counter man give hands-on instruction in high voltage and explosive gas handling.