Clutchless

iftekhar25, You already had your transmission serviced by a professional, they just did not work for Toyota/Lexus. That does not mean they were not competent to work on your vehicle. There are millions of vehicles with this transmission and many shops know how to service them properly. If you look at ratings of car repair shops you will see that dealers are almost always rated far lower than independent shops for quality of work.

So if your transmission shifts fine after the service by the independent mechanic then you have nothing to worry about as they adjusted the fluid level properly. Just continue to drive it and get on with your life.

FYI you can drive 10 miles on new fluid on a vehicle with 30,000 miles and it will look dirty again. That visual analysis means little.
The claim that it looks dirty is probably a lie about actually looking at the fluid, and is a sales technique as pointed out by RX in NC.