More than 40 cars parked on the forecourts of three well-known dealerships were damaged in one night.
Vandals caused tens of thousands of pounds worth of damage at the Chorley, Preston and Wigan branches of the Chorley Group.
They smashed windows, damaged cars and stole satellite navigation cards from some of the vehicles, many of which were Nissan Jukes.
The three incidents all happened overnight and police are investigating.
But managing director Pauline Turner is determined to battle on despite the “sickening” attack.
She said: “The break-in has come as a shock to everyone, but the team have really rallied around to minimize the impact.
“Today is our quarter-end so it’s one of the busiest days in our calendar year. We’ve also got a major used cars sales event taking place this weekend so it’s fair to say the timing could have been better.
“But everyone here is determined to make sure that mindless thugs don’t win the day so we are pulling out all of the stops to ensure the sales event goes ahead as planned this weekend.
“As far as we are concerned it’s business as usual at Chorley Group.”
Anyone with information about what happened is asked to call Lancashire Constabulary on 101.