We learned about Carla from Rick Steve's Rome book, and we were very fortunate being able to tour with her on those days we wanted. We did a tour at the Colosseum, San Clemente Basilica and the Roman Forum. We then did another at the Vatican Museum / St. Peter's Basilica.
The 4 of us, including two school aged kids were thoroughly impressed by the depth of knowledge and the amount of energy Carla has! Yes, that's a lot a lot of positive energy that reflected her passion for what she does. It was certainly like touring with a Roma local who can't wait to share all the good things about the city she loves. She also helped us out in detail for recommendations on where/when to go to for good food and stuff, even after all the tours were over.
She is also very good at controlling the tempo and to keep our kids engaged. Our kids are naturally interested in ancient history of Rome but still, we were impressed that at their age (primary and middle school), they kept their attention with Carla through these 3-4 hours long each, non-stop walking tours -- and one of the outdoor tours was done when it was raining!
Last but not least -- remember the good old days doing business when people really honored their words more so than a contract etc.? That's how it felt like working with Carla when we booked her time, and all the way throughout. No middle man or cranky billing company / web portals / mysterious, thousand-miles-away customer service involved. You communicate with her via email directly and things got settled nicely, straight and clear.
We highly recommend having Carla Zaia to tour Rome. Rick Steve's book is superb too for self-touring, which we did ourselves for many other sites there. (By the way, we also used Lonely Planet for more restaurant / Gelato recommendations, but Rick Steve's is much better as a "tour guide book" as you stroll through the sites) But, for places with too much to see under limited time, and especially when traveling with kids or in a group -- we felt that the time would be much better spent with a professional guide, like Carla. Here's her email for anyone who might be interested: