I'd be more likely to buy or sell a house on my own than to try to hook somehitng to a gas line. If I buy the wrong house, my wallet takes a hit. If I hook up the gas line incorrectly, my house explodes and my kids die.
I do agree with you that having a good real estate agent is important because they save you a crap load of work and know a bunch of questions to ask that most of us won't think of, but I don't think people who want to do it on their own are going to be convinced that an agent is doing all that much.
