(a) don't care about the quality of, because they are either frivolously cheap or you are able to to the necessary 'QA' repairs and inspection yourself (for me these are things like circuit boards and household consumables);
(b) something you already know you want that specific thing of and the shipping speed and return policy make them the best online option;
(c) are only buying because you found it somewhere else and you didn't know you wanted it until you were told about it (deal sites like slickdeals are where I encounter this);
(a) don't care about the quality of, because they are either frivolously cheap or you are able to to the necessary 'QA' repairs and inspection yourself (for me these are things like circuit boards and household consumables);
(b) something you already know you want that specific thing of and the shipping speed and return policy make them the best online option;
(c) are only buying because you found it somewhere else and you didn't know you wanted it until you were told about it (deal sites like slickdeals are where I encounter this);
then amazon is fine.