It does make sense to look at the domain for a website. In the United States - but nowhere else - government institutions are in the ".gov" domain; in contrast, www.nationalparkreservations.com
is in the ".com" or commercial business domain.
It can also pay to read the fine print, such as this notice right on the home page (although in deliberately hard-to-read text) of that commercial booking service:
National Park Reservations is a reservation service providing lodging and activity reservations. National Park Reservations is not an authorized concessionaire of any National Park nor are we in any way affiliated with the National Park Service of the Federal Government. For this service, National Park Reservations charges a ten percent non-refundable reservation fee based on the total dollar amount of reservations made.
The equivalent federal government domain in Canada is ".gc.ca", and includes the Parks Canada
and the Parks Canada Reservation Service