Addict invested in retro fashion bags (8)
I believe the answer is:
trousers
'bags' is the definition.
(I've seen this before)
'addict invested in retro fashion' is the wordplay.
'addict' becomes 'user' (I've seen this before).
'invested in' means one lot of letters goes inside another.
'retro' says the letters should be written in reverse (retro is Latin for 'backwards').
'fashion' becomes 'sort' (I've seen this before**).
'sort' reversed gives 'tros'.
'user' inserted inside 'tros' is 'TROUSERS'.
(Other definitions for trousers that I've seen before include "Outer garment" , "Corduroys or chinos" , "Leg coverings" , "suit section" , "Pants" .)