Guernsey Police are investigating after was caused to around 20 vehicles at Thompson Motors.
Investigating officers believe an incident occurred at Thompson Motors in the Castel between 4am and 5am on 28 May.
They have CCTV footage, but are asking anyone who may have heard or seen anything to come forward.
Michael Graham is the owner of GM Motors, who work out of Thompson Motors.
He says he was woken by police and shocked by the damage.
"Windows have been smashed, lights have been smashed, body panels have been hit by hammers.
"The cars are in a really really bad way.
"About a hundred and twenty thousand pounds worth of vehicles have been damaged.
"That's my livelihood, not having vehicles for sale, whilst waiting for the insurance to sort itself out is obviously going to impact me very badly.
"I'm still trying to come to terms with the fact that this has happened.
"We've been clearing up glass from the floor and put some covers over the windows so the interiors don't get any worse than they already are.
"It's a sickening thing."
Information regarding this incident should be reported to the Criminal Investigation Department on 222 222 or to Crimestoppers anonymously on 0800 555 111.
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