Indicate for yourself those topics that you are an expert in and check their popularity on these sites. For example, if you want to create a tour in London and you are deciding between Jack the Ripper, Harry Potter, Gangster London, and Windsor Castle tours.
According to the number of reviews, the Harry Potter and Windsor Castle tours are among the most popular ones. Jack the Ripper is also in demand. However, Gangster London is the least popular option and probably won’t be selling as well as the other three.