A little off (5)
'a little off' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for amiss that I've seen before include "Mistakenly" , "In an inappropriate way" , "(Gone) wrong" , "Not quite right" , "Haywire" .)
(Other definitions for on sale that I've seen before include "Available for purchase" , "available in store" .)