I trust myself. I don't think I've ever trust handing my tank over to a glass shop without them signing off that they guarantee they won't screw it up.
With a Dremel and a $15 diamond tipped bit from Home Depot you can drill for all eternity. albeit your first hole always takes too long.
I've done a total of 7 holes in 10 gallon tanks and never had a problem - it's really,
really easy. Just time consuming. A hole with about a 2" diameter took a good 10-15 mins on a 10 gallon tank. Thicker glass? I can only imagine.