Liquid was poured into the engines of two cars that were for sale while the owners were distracted in Ely and Cheveley.
Both vehicles were viewed by prospective buyers, two men, between 7pm and 8pm on July 2.
The liquid caused severe damage to the cars' engines, allowing the men to offer a lower price, but neither was sold.
Police have since released CCTV images in connection with the criminal damage.
Report information through the force website using reference 35/47629/24 or call 101.
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