Unfortunately, the tourists who had their fingers taken are in no position to type and confirm your paranoia!!

:-) Sorry, couldn't resist! :-)

Private car service and an reasonable SUV rental once you factor insurance, GPS rental and gas are probably going to be fairly close in price on this. If they go the private driver route I'd recommend that you offer them the taxi boat lake transfer from Monteverde to Arenal, as it will save some transfer time as well as being almost a tour in addition to a transfer service even though its not private. All of the activites you listed with the exception of the waterfall (on own) would be available with included transportation (and you can do the waterfall with transportation included through several different companies as well), and unless they want to do additional exploring on their own, its reasonable enough to take cabs or even walk from Si Como No in monteverde, fortuna and manuel antonio to get to local restaurants, etc, so as Crfan mentioned, it would really depend on the comfort level of the clients with driving themselves around and how much they think they'll use car outside of driving from point a to point b, and I would make sure as joyceh mentioned that the space is actually confirmable for the time frame you're looking at if the trip is for this Dec and not Dec 2013.

While in Monteverde just a few weeks ago, we stayed at Casa Batsu, a B&B in Monteverde that was just .... well, amazing. You will not find any other like it. If your clients are interested in a hotel that is similar to a US hotel, that's one thing. But visiting Costa Rica is an adventure in culture - you will not find a warmer, more friendly culture anywhere!

We ziplined with Sky Trek in Arenal and had a wonderful experience. We also did the Hanging Bridges with them and were impressed by the knowledge of the guide and the safety precautions they took (ONE of us is afraid of heights.....).

First, I don't see zip-lining on that itinerary, so I'm guessing it's an optional bonus?

I don't know about loss of limbs, but I can see how someone who did not pay attention to the safety instructions could lose a finger on a zip-line tour. It is always prohibited to be under the influence of alcohol or drugs, and you must understand that you are undertaking a risky activity and PAY ATTENTION to the safety instructions.

It's always best to check out the company and its safety rating before going on adventure tours. That said, I *believe* SkyTrek, which operates out of Monteverde and Arenal, is a reputable company.