Hi,
'I bought apples, pears and oranges'
Yes, I doubt anybody would think that pears and oranges comprise apples, but are there any disadvantages to putting a comma before and? No, I can't think of any except that you are adding unnecessary clutter to the sentence. However, I would never put a comma there in this sentence.
In truth, I was taught never to use such a comma, so it looks odd to me. A comma represents a pause, and the word 'and' itself acts as a pause, ie the word 'and' slows the reader's mind and eye down when looking at the sentence. So if you put both a comma and the word 'and', it seems to me that you are using two consecutive pauses.
The first time in my life that I even encountered any suggestion that one might put a comma there was just a couple of years ago when I started reading this Forum. So, please don't get the idea that every English writer uses such commas.
Best wishes, Clive