To save everyone from reading a super long post, I'll cut to the chase as far as background info goes: My wife and I just came home from a 10 day cruise in the Mediterranean, plus a couple of extra days in Barcelona. We didn't buy a ton of gifts/souvenirs, but we were coming home with more in the bags than we left home with. Our return trip was BCN-LHR-DEN (on BA), then DEN-STL (on SWA) after a overnight stop. (the stop was intentional to provide us some sleep, and prevent a 'don't get to STL until 2am' scenario)

Knowing that we'd have to re-check our bags, we carefully re-packed everything, and triple checked our bag weight. Each of our two check bags rang in on our travel scale at 49 pounds.

Upon arriving at the check-in counter, things went south quickly. I'll summarize as follows:

Me: Coming back from 2-week intl. trip. Triple-checks each check bag with scale. Both weigh 49.
SWA ticket agent: Nope, I have 50.5 & 51.
Me: My scale says otherwise. I 3x checked it.
Agent: Re-pack or pay $75 per bag.

**frantic and frustrated re-packing ensues**

Me: Takes one pr. jeans out of each bag, transfers to carryon. Bags reweigh at 47 and 48.4.
SWA agent: I have 49 and 49.5.
Me: ... that's where I was before. Check your scales.
Agent: *stares blankly* um, ok.

Cherry on top: The extra jeans made the carry-on hard to scan, so of course TSA manually tosses the bag like a jail cell, forcing us to repack a bunch of fragile gifts from our trip.

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Now, a few points I wish to make in summary:

1. I acknowledge that the airport scales are certified for use, and higher-grade than the scales we buy for home use. My scale has served me well for years, and this is the first time I've had an issue, fwiw.
2. Were I many pounds over on their scale, I'd concede the point (and I would guess that my scale would have said similarly before I even got to the airport). BUT, even if SWA's scale was dead-on, it's ~1 pound between two bags. After coming back from a long intl. trip. Have some damn mercy.

3. Barring any mercy being shown, I suggest one/both of the following need to occur:

A) passengers be given a 1 pound buffer on weigh-in, especially if transiting home from intl. travel.
B) some company designs/sells a travel scale that meets the same accuracy standards as the ones used in the airports. That way, passengers can have more confidence that their scale is giving a reading that won't be contradicted at the airport.

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Personally, this whole thing was pretty much the last straw for me and SWA. Their cattle-car boarding has always been a PITA, but I used to overlook it because they flew most everything that was NS out of STL. But after all of this, I am sorely tempted to go back to multi-stop AA routes. At least their folks don't seem to jerk folks around for a (questionable) pound of bag weight.

And before someone says it... yes, I know the current rule says 50. And I always adhere to it. That's why I bought a scale, and measure my bags multiple times. But my larger point is that either pax need a buffer zone on that, at least in limited scenarios, or the scales we all buy and use need to match what the airport scales can do.