Flush it yourself,

Unless you will be able to watch the shop do it for you. I paid a vlvo shop to do this and all they did was drain the three or so quarts out of the pan and refill it. As the atf was visibly dirty it made no difference.

It is really easy to do. You just need to buy one piece of clear tubing for about two bucks and buy a couple more quarts of ATF than you think you might need. Like around 16 quarts just to make sure.
It is really easy to do. Maybe spray the nut at the radiator where you will be breaking the line open a couple days before hand to ease the loosening of it.
You need a good funnel that will fit fairly tight into the fill tube, I arranged mine by wiring it onto the hood while it was opened so that I could leave it unattended while it was full of atf while I changed through the gears and changed the container that I was draining it into. If you are doing this when it is cold out the clear tubing will be hard to work with.
Good Luck.