It also applies to cruise "lines".
It could easily cost more money using a TA. Some charge cancellation fees and change fees that are not originated with the cruise line. With the new Carnival pricing Carnival seems to be catching on.
It could easily cost less using a TA. Some still give kickbacks out of their commissions.
In either case, many TAs are not available 24/7. I don't know that any PVP is, however, individual reservations at Carnival always are.
, is not eliminated by using a credit card. There are time limits. Once I put a deposit down on a cruise with a 1 ship cruise line. The ship sank, and with it my deposit. I got back not dime one.
It is only a stretch if it doesn't happen to YOU.
Best price is relative. Group prices are group prices and not a guarantee of anything.
I usually do use a TA, but I also look after my best interest. There is never, EVER, a compelling reason to only use a TA or only use a PVP. Individual mileage may vary.