We booked several via the chief concierge in our most recent trip.

1) trekking, we had a good time trekking. Nothing too strenuous but nice walking through the countryside/ jungle. We felt the visits to temples were too long/ not needed but the trekking part was nice.

2) Flight of the Gibbons, fun if you like ziplining. If I recall, price through concierge was the same as if I booked through FG directly. I think we actually only paid at FG and they gave us a bigger discount than I expected.

3) Bicycle tour, we took the easy one, 25 km. All flat. Not beautiful at all, as you go through paved roads through villages. Stopped at a school. And a carving factory. It was ok but nothing special.

Everything was booked in cash (no credit cards...) to the tour operators directly.

In past trips, I booked through agencies around the hotel. We did a white water rafting trip that was awful. There were little rapids until one part where we turned over. Turns out one of th girls in the boat couldn't swim and freaked out. Pulled me under (scary) until I knocked/ punched her off. Then I went to help her. I lost my glasses. THere was no real safety training anything. I would not recomment this.