Upset about fancy car – it is unreliable (7)
I believe the answer is:
erratic
'unreliable' is the definition.
(similar in meaning)
'upset about fancy car it' is the wordplay.
'upset' shows that the letters should be reversed in order.
'about' becomes 're' (common abbreviation for 'with reference to').
'fancy' indicates an anagram.
're' in reverse letter order is 'er'.
'car'+'it'='carit'
'carit' is an anagram of 'ratic'.
'er'+'ratic'='ERRATIC'
'is' acts as a link.
(Other definitions for erratic that I've seen before include "Sporadic" , "Not regular in pattern" , "Deep affection" , "Rambling" , "Irregular in motion or habit" .)