Some wulin duels are clearly intended to be private: uninvited observers were not welcome at the Mt. Hua Sword Tournaments and I think any intruders would have been dispatched by the Greats. Other wulin duels are accessible to an elite group of invited spectators, such as the individuals who were privileged enough to witness the Sai Mun Chui Sheut/Yip Goo Sing duel on the roof of the imperial palace.
Were there many other duels, however, wherein the general public was not only welcome, but actively encouraged to attend? Perhaps it's part of some general demonstration, or even a sort of early commercial entertainment where a fee would be charged for admission.