We used Carlos Zarate tours for a personal guided climb of el volcan Misti in Sept 2012. We found their service to be extremely professional and, most of all, experienced. We were very impressed by how many times they had made the trek and how easily the "helpers" who carried all our gear to the camping site on the first day, made multiple trips and hopped up and down the volcano with ease while we struggled with altitude to do the minimum. They provided us with top quality gear, set up and broke down our camp, cooked us a hot dinner and breakfast (which, honestly, at that altitude you can hardly appreciate as eating is NOT easy, but it was nice they tried!). We got a late start on day 1 due to some minor car trouble they had, so we were still walking when the sun dropped behind the volcano and the temperature dropped - but the guys went through our backpacks (they'd taken ahead to the camp site) and brought us back warm layers since they knew we would freeze otherwise. The climb was incredibly difficult, and being healthy but not conditioned or trained, we climbed slower than most. Our guide was no cheerleader or emotional motivator- he was mostly mute and often mentioned "This is how far some/most people get..." quite often to slightly nudge us toward turning back, since we were taking too long. However, he let us continue trying since we weren't giving up (he also was in on my then-boyfriend's plan to propose at the summit so I think he gave us an extra grace period) and we did finally make it to the top. Since it was so late, we had to race down (beating the sunset was crucial) and at one point he got out of our sight and we had to stop and whistle until he realized he'd lost us and returned to show us the way (getting down is just as risky/scary as climbing since there is no obvious path!). Other than that one brief lapse, we felt he guided us with utmost confidence, knew the volcano extremely well, he helped us navigate the ice/snow when necessary, and we were never in danger. We did regret following their suggestions about how much water to bring - we'd planned for more but they told us to leave it in the car as it was too much...ended up we ran out shortly before the summit, and were very dehydrated on the trip down (the guide kept telling us - eat chocolate, it goes straight to your legs! But we would rather have had water!) but one of the guys came running to bring us water for our last 1/2 hour stretch toward the car which was also very nice. Without such excellence, I'm sure we wouldn't have made it to the top and wouldn't have had the amazing memorable proposal experience we did. We were very glad we chose this tour provider for our trip.