Unreliable and expensive cover for Alpha Romeo (10)
I believe the answer is:
precarious
'unreliable' is the definition.
(thesaurus)
'expensive cover for alpha romeo' is the wordplay.
'expensive' becomes 'precious' (I've seen this in other clues).
'cover for' means one lot of letters goes inside another.
'alpha' becomes 'a' (phonetic alphabet: alpha, bravo, charlie etc.).
'romeo' becomes 'R' (phonetic alphabet: alpha, bravo, charlie etc.).
'a'+'r'='ar'
'precious' enclosing 'ar' is 'PRECARIOUS'.
'and' is the link.
(Other definitions for precarious that I've seen before include "Uncertain; likely to fall" , "having difficulty remaining upright" , "Highly insecure" , "Not having a steady position" , "Hairy" .)