First off I agree that the fees are excessive so I sympathize with you there.

In terms of being transparent though - United does do a pretty good job. If you put EWR - RDU into the baggage calculator they have on their checked baggage website it nicely lays out the fees and then has a click button that then shows additional fees beyond the standard $25 for a 50lb pound.

That being said the calculator itself actually says that the overweight fee for EWR - RDU is only $100 extra if under 70 pounds. If you got charged more as noted above I would file a CC charge-back and simply print out the information from their website (link is below) and you ought to be refunded at least down to $100 from the $125. I would also email United with a complaint and attach a PDF of the website to show the overcharge. Based on the calculator you should've paid a total of $125 - $25 for bag fee + $100 extra for overweight but under 70 pounds.

Going forward I would suggest buying a luggage scale from Amazon. You can get them for under $10 and while they might not be 100% accurate they do a good job of giving you a general sense of whether you are close to the 50 pound limit. I have one that I always use with my checked bag to get a sense of whether weight might be an issue.

The baggage calculator for United is here: https://www.united.com/CMS/en-US/tra...edBaggage.aspx