Sorry about your LBS. Guess they don't want to stay in business, I certainly wouldn't go back. Another thing. I have over inflated a bike tire/tube to failure. And while it will blow spectacularly, it does so at the point of over inflation. Not 5 minutes later.
My 2 cents on tire mounting. If you're real paranoid. Once you get the tube inside the tire and the tire on the rim, pump it up just until the tire takes on a firm shape. Let all the air out. Now while holding the wheel by the rim, break the bead between the tire and rim by pushing on the sidewall with your thumbs. Look inthe gap for any sign of a tube. Do both sides. If there's none inflate the tire to the correct pressure. If there is, pop off the tire at that spot and push the tube under the tire and try again. A pinched tube will give you plenty of warning with a bulge, if you take it slow.