For information on visiting Bryce Canyon and Zion during the winter months, visit the National Park Service sites.
http://www.nps.gov/brca/
http://www.nps.gov/zion/
People visit the national parks year round. Each season offers something special. And during the off season, you can feel like you have the park to yourself.
When searching for "Lake Powell Tours", "Bryce Canyon Tours" and "Zion Tours", I saw a number of results for companies offering their services. If you are looking for a single tour operator that will take you to all 3 places, you will likely have difficulties. Most tour operators in the U.S. focus on a single destination.
As for booking online, for the most part, I think it is safe. I have only heard compaints about one company who customers felt that they had been cheated by. That company was not a tour company.
You can search for tour operators on the Utah State Tourism Office site. http://www.utah.com/guide/result0.htm Choose the location and type of tour you want. Because they are listed on the Utah state site, you can feel secure in the legitimacy of the business. The number of tour companies they list is only a fraction of all the companies out there. If you want more choice, do a google search. The quality of the site can be an indication of if you can trust the company. Is their online reservation process secure? Do they provide comprehensive contact information. Is their cancellation policy clear? Is the service provided clear? Many tour operators will add a fuel service charge, security screening fee or other fees, depending upon the type of tour. Is that information available?
You can also check with the Better Business Bureau. http://welcome.bbb.org/ Not every business will be listed here. But if a company operates in an untrustworthy manner, you can find out about it here because they will likely have had complaints from past customers. You can search by the company name, address, phone number or website address.
Good luck!
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