Ok, like carnut, and the other guys who own or manage shops we deal with “unhappy” customers from time and time again.
Here is my first question:
When you left the shop and changed gears the first time did it grind?
2nd question:
If it did grind, did you turn around and ask them to take a look at it?
3rd
How many miles were on the tranny? 40k?
Here is the way I look at it. If the car was grinding gears the minute you got in the car and changed the gears the first time, you should have brought the car back to the shop and asked what was going on. If you had the car for a week and then the cars tranny started to act up, then the shop is not at fault.