The best advice for someone considering installation and maintenance as a career, especially in Home Theater, is to really learn the product. Not just what you plan to sell and install. When you can answer questions to the customers comfort level they are usually not so critical as you are working. I doi recommend this as a rewarding and challenging career, one that I would choose again. The pros about this type of career are getting to meet many people. Getting to play with many home theater products you might never be able to afford yourself, and learning waht will go best in your own home. The cons are that people can be very demanding and unfortunately sometimes dishonest.
