I bought a luggage scale from Amazon a couple of years ago for about $8. It has proven to be very accurate . . . always matches the scale at the airport precisely. It's a much better method than the "stand on the scale without your luggage, now stand on the scale with your luggage" method. Twice a year, I bring two checked bags to Europe with stuff for my daughter, and I usually maximize my allowance . . . two 50-pound bags. With this luggage scale, I am totally comfortable and confident when they weigh in at 49 lbs at home (I leave a 1 lb margin of error, but truth be told I've never needed the margin).
Many years ago (mid-2000s), I was a couple of pounds overweight on a checked bag, but the check-in agent let it slide. Maybe they're playing it more "by the book" these days.