i usually do a bit of research online 1st to see where places are, how to get there etc
and try not to use either where possible.

for example

Xcaret park in Mexico was literally a few minutes away from our hotel,yet the reps were selling it with transport and adding comission

it was far cheaper to make your own way by taxi,leave whatever time you want to and not have to wait around on coaches

Think there are pros and cons to both ways but i like a bit of fun adventure and like to use local transport etc.

would prob go with hotel rep over a beach seller tho