You have to take every shop on a case by case basis, including dealer shops. I have a Ford dealer near me that I don’t visit anymore. On two separate occasions I brought them different vehicles for transmission diagnosis. On both occasions I was told that I needed a new transmission. On neither occasion was this true. Especially on older vehicles, a lot of shops won’t mess with transmission issues. If there is any hint of a problem they just go the all or nothing route.
At this age and mileage, other than complete abuse, I’m thinking only a few things would lead to the need for replacement, and they wouldn’t be all that common this early on. One is just some fluke as noted by ok4450 - basically bad luck on early part failure. Another is if you blew a cooler line or seal, lost the fluid and kept trying to drive with the transmission slipping. That will kill it fast. The only other one I can think of is an internal radiator leak that puts coolant into the transmission fluid. That will also kill it fast. Short of something like that, I’d first assume a problem that wasn’t catastrophic.