First of all, not everyone can just become a private tour guide in Europe or South America. It is much more than simply paying a fee for a license to run a tour. In Europe and South America, a professional tour guide is just that - a professional. Most guides need to study countless hours and pass a battery of examinations to become licensed. Some guides are even required to speak multiple languages. They may need to meet other requirements, such as take follow-up courses in order to maintain their licenses.
The Traveling Professor highly recommends hiring a licensed tour guide, especially to introduce the traveler to a city or a site. On The Traveling Professor small group tours, we have found professional tour guides especially useful and informative on our tours to Paris, the Normandy Invasion Beaches, Ireland, Iceland, Italy and all other destinations we travel too.
Of course, you can do the research on your own and act as your own tour guide. However, The Professor's extensive travel experience tells him that no one can give the expertise, insight, local flavor and tips that a good, local guide can provide. Not only do they know the history, culture, and their way around, they will also help with dining tips and activities to do when you leave the tour guide and go on your own. No guide book or audio tour can substitute for the knowledge and interaction a real, live tour guide provides.
That is not to say a tour guide is necessarily needed for the entire trip. In some cases, like an introduction to a city like Bergen, Norway, our guide gives us an overview of the city. The traveler finds it invaluable for the rest of their self-guided adventure in the city. On our small group tours to Florence, for instance, we do essentially the same thing. We get an overview of the city and travelers then set out on their own. But in some cases, when travelers have a particular interest in something like the Uffizi Gallery, we arrange for a knowledgeable and engaging guide to tell the stories behind the sculptures and paintings. At the Normandy Invasion Beaches, there is nothing like having a guide to tell the stories and visit the sites that just cannot be found in the guide books.
One thing to consider when hiring a professional tour guide is the expense involved in hiring a guide. Of course a way to cut down on the expense would be to have a small group of travelers splitting the expense of the guide, but The Professor does not recommend having a group size of over 15-17 travelers.
Many cities, London comes to mind, have organized walking tours led by professional licensed guides that travelers can join. These can be great. However, the traveler needs to know that since participants outside of you or your group will be on that tour, there is probably little opportunity to tailor the tour to your interests. Also, group sizes can be large.
Where can you find a licensed tour guide? The best place to get a licensed tour guide is through a recommendation by someone who has had a favorable experience with a guide. The second best place is to ask the hotel where you will be staying. Sometimes at travel shows, licensed guides are available to speak with. You can contact those companies that run open walking tours of a city and ask them if they can provide a private guide. Visitor information centers sometimes offer the names of licensed tour guides. Last, but not least, there is the website ToursByLocals.