What I do - get yourself some of that foam pipe insulation. Cut two short pices, and fit them over the jaws of a vise. Lay a folded towel or washcloth between the insulation in the vise. Run the braid thru the fold in the towel, thru your rod guides, and onto the reel.
Tighten down the vise to put tension on the line. Wearing a glove, hold the line between your thimb and forefinger on your non-crank hand above the reel, and start cranking. Adjust the tension on the vise as needed (as the line travels thru the towel, you will have to tighten down a bit a couple times, as it wears the towel.) This will make the line tight enough so that you can fully load the reel.
When fully loaded, to be sure I get it as tight as possible and get it to lay correctly, I then take the rod and reel over to my neighbor's driveway. I tie on a jig or a hook, and hook it to his truck bumper. I then walk off as much line as I can (preferably all the way to the backing.)
I then pull tight, as if fighting a fish, and keeping tension on the rod, slowly walk forward until it is all re-spooled. The line will lay as best and tight as it ever will. Works like a charm for me.
And not to take anything away from shop owners, but I never quite understood the advantage of having them spool your reel (other than convenience). Once you make a cast, and reel back in, all of their tedious work has vanished......