Searching by price the only option for a certain flight this weekend was a full J fare. I searched by schedule and was offered the same exact flight as an I fare. I searched by price again and was offered a C fare. I ran the search by schedule again and got this error message when I selected the flight:
We are unable to process your request. Please call the Delta Online Customer Support Desk at 1-888-750-3284 for assistance. Customers outside of the 50 United States should contact the Delta Reservations Sales office for their country. (#101728)
I never feel confident I'm getting a good price from delta.com, my searches for the exact same flight came up with three drastically different prices in under 15 minutes.
I tried again and was able to get the I fare back by searching for an economy fare based on schedule, since coach is sold out. If I search for a Business fare or by price I still get stuck with a C fare.