Maui stores selling discount activities?

I was in Maui and saw many stores selling discount activities. In Lahaina, there seemed to be one of these places every other store. (eg. Zipline fun for $85 while regular price: $120; Luau at the Hyatt for $20 when the regular price is $85). How do these things work? They sound too good to be true.



Do they all involve something like listening to a 90 minute timeshare presentation? Or are they simply good deals that travelers should take advantage of? Thanks!
Many are likely doing something like selling timeshares, so yes, there