Simpleton runs hotel in Scottish city commercial (10)
I believe the answer is:
dunderhead
'simpleton' is the definition.
(dunderhead is a kind of simpleton)
'runs hotel in scottish city commercial' is the wordplay.
'runs' becomes 'r' (cricket abbreviation).
'hotel' becomes 'h' (phonetic alphabet: alpha, bravo, charlie etc.).
'in' is an insertion indicator.
'scottish city' becomes 'Dundee' (city in Scotland).
'commercial' becomes 'ad' (abbreviation for advertisement).
'r'+'h'='rh'
'rh' put into 'dundee' is 'dunderhe'.
'dunderhe'+'ad'='DUNDERHEAD'
(Other definitions for dunderhead that I've seen before include "dumbass?" , "Idiot" , "Dunce" , "fool" , "Ignoramus" .)