So for the tour itself I can not say, but for the meeting point and the unprofessional behavior of not even trying to contact your customers when they have not showed up at the exact spot in time is the reason for this bad review.
So let me first give you the "directions" we were told to follow:
"Outside of the National Archives at 9th and Pennsylvania Avenue NW
Meeting point is at corner of 9th Street NW and Pennsylvania Avenue NW
800 Pennsylvania Avenue NW
Washington, DC
DIRECTIONS
Across the street from the National Archives/Navy Memorial Metro Station"
So here's 3 different directions, we stood on the corner of 9th and Pennsylvania
20min before departure, I was looking for any person looking like a tour guide, even crossing the street several times to ask random people if they were there for a tour, but I could not see anyone. I could see some busses on the other corner of the next street, but that was not were we were directed to go and I was waiting for them to call me so I could get a more detailed direction, time for departure came along, and noone tried to contact us. I tried to call them, but I was sent straight to voicemail, I left a couple of messages, but no reply.
After a good 45 min I called Viator to get a refund and started planning for something else for the day. The company called me an hour later in regards to my messages, the person calling me did not seem apologetic and said it was impossible I missed their 3 busses, I told him that if he would have called me at departure time to tell me this, maybe this whole situation would never have occur. So my advice to this company is to have better directions on where the meeting point is and give customers better indication to what to look for, and if people are not there in time, call them!