I haven't paid for any such work, but I've rebarreled four of my rifles, and I've performed all of the 'blueprinting' types of clearancing that allows the rifle to shoot it's best. Much of a Garand's accuracy is in the barrel and in whether or not the sights move around. A stock barrel will shoot very well if it's not excessively worn, and with young troopers busily cleaning their rifle for some drill sargeant's inspection by madly and desperately pushing a steel cleaning rod into their muzzles many of the rifles have larger than ought to be muzzles.
If the gas cylinder is loose on it's cuts at all the front sight can wave around enough to make for wide groups on target, and the rear sight aperture can also wiggle in it's track causing the same errors.
For a John Garand match legal rifle these are about all that can be done - the stock needs to fit the action snugly, the trigger group should clamp firmly, and the forward stock pieces should have a little room to move for and aft so as not to put a crimp on the barrel.
For high power match shooting where bedding is legal then a COMPETENT job of glass bedding the action can be worthwhile. The action/barrel needs to be exactly on line axially and not pressured in any direction by it's bedding or the rifle may not shoot well even with work done to it. Some HP shooters hog out their foregrips to paper thin in the hope of it not affecting their barrels but whether that helps and how much is questionable. There are a few little fitting tricks to help let the barrel stay free of onwanted loads as it heats up but in general I've just told you all about accurizing a Garand rifle.
I do think that the higher price of a certain brand of barrel is worth the money in order to get the last bit of accuracy from a given rifle, but only if the rest of the rifle is very well put together. For all others some of the less costly aftermarket barrels will work surprisingly well in the guns.