The same trip can vary by 60% in price depending on where you buy it, and by more in quality.
The same boat, on the same day, with the same guide, is routinely sold at three different prices. The hotel desk is the most expensive because it carries the hotel's commission; a street office is the cheapest and the most variable; booking direct with an operator sits in between and is usually the best balance.

Price is not the main thing to compare, though. The questions that actually matter are: what is included, is hotel pickup part of it, what is the group size, and what happens if the trip is cancelled for weather. A trip that looks €10 cheaper and then charges for lunch, entrance fees and the return transfer is not cheaper.
On hotel guides: some will tell you that outside operators are uninsured or unsafe. That is a sales technique. Any licensed operator carries passenger liability, and your own travel insurance is valid throughout the country.


The questions that actually matter are: what is included, is hotel pickup part of it, what is the group size, and what happens if the trip is cancelled for weather.
What to check before paying: a licence number, a written confirmation with the total price and what it covers, and a phone number that a person answers. Pay a deposit rather than the full amount in cash up front where you can, and keep the confirmation on your phone.

