Protected customers sounded off endlessly about goods? Quite the opposite! (10)

'protected customers' is the definition.
(customers given a warranty)

'sounded off endlessly about goods? quite the opposite' is the wordplay.
'sounded off' becomes 'ranted' (to sound off is to rant or complain).
'endlessly' means to remove the last letter.
'about' indicates putting letters inside.
'goods?' becomes 'ware' (I've seen this in another clue).
'quite the opposite' becomes 's' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'ranted' with its last letter removed is 'rante'.
'rante' going into 'ware' is 'warrantee'.
'warrantee'+'s'='WARRANTEES'