Raw Coins To Send To NGC?

I was just curious how good your luck has been with raw coins (Merc Dimes) sent in to grade at NGC? I have an almost complete set I want to certify, but I am afraid of too many of them coming home in a body bag from being 'improperly cleaned' or some such none sense. This has happened to a few raw coins I have sent in the past. I was wondering how good a chance I have of getting them slabbed from raw stock. Anything in particular to look for? Do I need a stronger form of magnification? Hmmmm, not too sure about sending money down the drain for cleaned coins.