Unreliable, making endless mistakes I see (7)
I believe the answer is:
erratic
'unreliable' is the definition.
(similar in meaning)
'endless mistakes i see' is the wordplay.
'endless' means to remove the last letter.
'mistakes' becomes 'errata' (an erratum is a mistake in a printed work).
'see' becomes 'C' (the word for the letter, according to Chambers).
'errata' with its final letter taken away is 'errat'.
'errat'+'i'+'c'='ERRATIC'
'making' acts as a link.
(Other definitions for erratic that I've seen before include "Rambling" , "Random, unreliable" , "Unpredictable; occasional" , "Unpredictable - car tire (anag)" , "Cartier (anag.)" .)