Don't know if this helps because I have 2 different instances. And I am like you, I always just changed it myself by dropping the pan and changing the filter
Took the daughter's car to a Valvoline oil change place. About 60K on the car at the time and they recommended the trans flush. Said OK. Didn't really pay attention to what they were doing but it sure looked like the new trans fluid was dark. Yep, 2 months later the trans is shot. Never going back.
On the other hand the Chevy dealer that does all my work convinced me to have this flush for my van. He said he personally witnessed a demo using their equipment and after it was done they dropped the pan to check the filter and it was clean. So far I've had excellent work from their service department so I did it with no bad effects. In fact it goes back in next week for another trans change. Probably do the Vette this spring.
This doesn't really help but I thought I'd tell you about my experience so far.
Good luck.
Ron
"Baldie88"