I just go some inserts in the mail and I'm not sure how to trim them.  My first try at it go the inserts in, but they don't have that smooth "pro shop" look to them.  In fact, they look pretty hacked up.  How do pro shops do it?
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Tisker- Looks like Tarzan, bowls like Jane
God bless the pessimist, for they bring extra ammo

Get the insert positioned so that one side is flush with the finger hole, and the other side is either flush or slightly raised above the hole.  I guess it depends on how the finger holes are pitched.

Glue the insert on 3 sides (I always leave the top open, in case I want to insert a shim), then take a sharp razor blade and, working from the "flush" side to the non-flush side, smoothly slice off the part of the insert that's above the finger hole.

It takes a little practice to get it right, so that it looks the way the pro shop guys do it, but that's the approach.  Remember, slice it smoothly, don't hack at it!

Get Turbo quads, then you won't have to do anything but cut off the end you're not going to use and glue them in right.  We usually glue the sides, because usually the sides are the only places that are pitched.  Start with the inside of the hole near the bridge, and make sure that's level with the ball's surface.  Then if you have left pitch in your left finger and right in your right finger (we do 3/8th's per hole) then after you glue the inside of the grip to the side, the opposite side should be sticking up just a bit.  You might get glue on your fingers, but if you push from the top of the grip instead of the inside, you'll get it a lot closer.  Everybody has their own techniques, but all of mine look near perfect.  Bigger grips and smaller grips are a problem, because the bigger ones are too flexible and they tend to bubble inside the hole when pushing from the top, and the smaller grips aren't flexible enough, so it's hard to push them in.  21/32 - 27/32 are the easiest to do, so if you fall somewhere in there, the technique might work.  

Then say you have reverse and left pitch in the left hole.  Glue the southeast part of the grip first and then the northwest, because those are the points that the two pitches are the closest, get it?
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I know Kung Fu!

I am the one, the one that will bring balance.  All the pins shall be destroyed!

Thank you for all the suggestions.  I wish I had posted this first!

Robert-
I haven't heard anything about a practice from Eddie or Cory.  We'll have to figure something out.
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Tisker- Looks like Tarzan, bowls like Jane
God bless the pessimist, for they bring extra ammo