Personally, I would never pack that close to 50lbs and expect my travel scale to match the scales at the airport. "49lbs" could easily be 49lbs 15ozs, and the margin of error be +/- 1 lb. Checking it 3x on an inaccurate scale just means you get the same inaccurate reading 3x.

If I were concerned about being over, I'd curb check, with a tip in my hand.

At least they let you repack and didn't just charge you $150.