It's not the TA's fault when ITA produces bogus quotes due to not using married segment inventory for multi-city. You are putting way too much trust in ITA's software. I can post demonstrations of this all day long. See below where ITA is showing E fare (with underlying L), but as you can see from EF, there is neither E nor L available on the married segments (only K bucket and higher has inventory).
This is one of my major complaints with delta, users cannot force the married segments like on UA and AA. There should be zero reason why a flight to a location is $220 on UA and AA and $720 on DL when travel is 200+ days out. They can most definitely force this but you have to find the right agent. I've had agents do it numerous times and it is almost never on the first call. I know this example is for 13 days out but the same concept applies.
Can you explain why if each leg has E9 but when they are together is E0? Because that does not make any sense to me. If the planes are empty, what the hell does it matter?