Are you sure they were really "worse"? There are people who come from different backgrounds, who will feel different things are better... I've seen some translations and even though they were done by natives into my native language, I would change something, because they just didn't feel "right" for some reasons.
Just ask a person from UK, US and Australia to translate some text into English. You're likely to end up with 3 completely different versions. The same thing will happen with different regions in the same country. For one person a sentence will be ok, for another it's something they'd never say, and for you it will look like an "irrelevant mistake".
Aside from the ones that took something that was correct and turned it into something blatantly wrong, you do raise an interesting point. However, I'd maintain that if you end up with linguistic inconsistencies and it's affecting your bottom line, then that's "worse" in my book.
I've learned that it must be made clear to the translator exactly what the target audience expects (I've had to tell British translators to use U.S. spellings, mainland Chinese to use terminology that's specific to Taiwan, etc.). The most experienced ones know of these distinctions and make sure to observe them. The ones who don't (or can't) are better reserved for the jobs that are matched with their background.
Just ask a person from UK, US and Australia to translate some text into English. You're likely to end up with 3 completely different versions. The same thing will happen with different regions in the same country. For one person a sentence will be ok, for another it's something they'd never say, and for you it will look like an "irrelevant mistake".