Trading Standards Officers at CNES are advising residents to be wary when purchasing vehicles privately.
The Comhairle said there are honest people selling their own cars, there may be also be dealers evading their legal responsibilities and misleading purchasers into thinking that they are buying cars from private sellers.
Vehicle traders can apply for a licence from the council.
Island trading standards have been monitoring private car sales within the Western Isles.
A spokesperson said: "Our intelligence shows that a small number of individuals may be advertising and selling several vehicles suggesting that these sellers are buying cars to sell on and, in the eyes of the law, are in business as car dealers.
"Cars sold by disguised traders may be defective, unsafe or clocked, and the unsuspecting consumer has little hope of any redress when things go wrong.”
The spokesperson continued: “We will continue to monitor local private car sales in order to protect residents from unfair trading practices.
Crackdown on unlicensed car sellers
31 October 2015