No it's not a faff for most sellers, though their terms do vary.
Put in a returns request or contact the seller directly through Amazon. Amazon sellers are given a target of 24 hours to respond to Amazon messages.
It depends what you mean by original packaging. The packaging for the item is essential. Things need to be returned in a new condition so they are fir for resale unless the item is faulty or not as described. (the picture being a little bit different is not good enough for this, it has to wildly vary).
The envelope that the item came in is not important and you can send it back in a bin bag as long as it is adequately protected.
If you are buying to try, ALWAYS remove the item packaging carefully and keep it.