Every other film advertisement is fake? (8)
I believe the answer is:
imposter
'fake?' is the definition.
('imposter' can be a synonym of 'fake')
'every other film advertisement' is the wordplay.
'every other' indicates alternate letters.
'advertisement' becomes 'poster' (I've seen this before).
The alternating letters of 'film' are 'im'.
'im'+'poster'='IMPOSTER'
'is' is the link.
(Other definitions for imposter that I've seen before include "Pretender, fake" , "One who makes deceitful pretences" , "Cheat" , "Charlatan" , "One pretends to be someone else" .)