Thank God I have well grammar.
In music, when a keyboard instrument is tuned such that it could be described as "well-tempered", the temperament used, if not equal temperament, is likely to be one of the class known as "well temperaments". This usage of "well" as an adjective still jars with me, but is fully established (well established - ha!) in the relevant circles, and has a specific meaning distinct from that carried by "good temperament".
As for Sam, that usage, though wrong, is also well established in many circles, sometimes in specific idiomatic phrases like "the boy done good".
However, graduate students from non-English-speaking countries tended to write the best English. I guess when you have to actually make the effort to learn something, you take care to use it properly.
The point being that idiom is more than merely correctness, and takes a lot longer to learn (or rather, pick up), also varying more according to circumstances. Simple correctness needs rules to define it, which in some senses language doesn't really have (they're added as a layer over the top by grammarians) - and which can lead, as Churchill remarked, to "the sort of language up with which I will not put [artificially avoiding the preposition at the end, in that instance].