My wife and I will be visiting Gettysburg in August, this will be my 3rd trip in 2 years and her first ever. Last year my son and I took the bus tour with a guide, and earlier this year we took the audio tape bus tour. This visit I think we'd like to get one of those licensed tour guides - I saw several of them with small groups of people on my last visit, and this seems like a great way to learn more about specific areas of the battlefield.
What's the best way to get a good tour guide? Are these guys private businessmen or are they working for the tourist center? I want to make sure we don't get stuck with a dud for a guide - does anyone have any recommendations?