Dealers under-using Facebook advertising, claim experts.
Dealers are also at risk from being ripped off by consumer car sellers.
SMMT figures show slight slowdown in car manufacturing in October.
Dealership group Lookers says profits from new car sales rose by 11 per cent in the nine months to the end of September, while the figure for used car sales increased by 22 per cent.
Vauxhall reveals new models due for release in 2017.