Salary
Average Salary: $23,770
Expected Lifetime Earnings: $992,350
Tour guide salaries vary depending on years of experience, the specific industry for which they lead tours, and whether or not they're willing to wear silly costumes. Guides working in the United States make between $17,000 and a little under $40,000 per year (source).
Clearly this job isn't going to make you rich, but making money doesn't seem to be the motivation for most guides. It's about using other people's money to travel and learn—and we're only sort of kidding about that.
Think about it; it's not just people visiting the British Lawnmower Museum (totally a real place) who need a tour guide. Tourists visiting Paris want a tour guide, people visiting the Great Wall of China want a tour guide, folks seeing the Statue of Liberty, the Louvre, and every other possible interesting, pretty, important, or historic place there is, all might want a tour guide.
They're looking for someone (you?) to give them an interesting story to take back home. You don't even need to be from the place, just know a little bit about it. You could quite literally go anywhere and do this job.
So while getting rich may not be in the cards for tour guides, they'll gain knowledge and have experiences that'll be tough to top.