Discount Hawaii tour websites

I have been planning which tours we want to do, as we are leaving in two weeks. After doing a search online last night, I came up with some websites that offer tours for discount rates.

Has anyone booked through these discount websites? Should I trust them, or pay full price through the actual tour company?

For example, the bike ride down Haleakala is 100 per person, through the company, but I found it for $70 per person somewhere else.

we rode down Haleakala and we booked it through the hotel, it was $105 per person. i would book it through the actual tour company. And ask if you can be part of the first group that goes down, so you don't have to sit around waiting.

the ride down the volcano was amazing, but wear lots of layers! it is FREEZING up there before the sun rises!