Charming woman that tests consumer products on the radio (5)
I believe the answer is:
witch
'charming woman' is the definition.
'that tests consumer products on the radio' is the wordplay.
'that tests consumer products' becomes 'which' (consumer magazine Which).
'on the radio' shows a homophone (sound like).
'which' is a homophone of 'WITCH'.
(Other definitions for witch that I've seen before include "Cauldron-stirring hag" , "Broomstick riderof children's tales" , "Wise, wicked, woman" , "charming female" , "... and magician" .)