Kwik-Fit has been left red-faced and reviewing its security procedures after two customers' cars were stolen from a site in one month.
A black Vauxhall Vectra belonging to Antony and Sharon Davey was stolen from the Tonbridge centre last week, and a Mazda MX-5 was taken from the same business four weeks previously.
The Daveys had been instructed by staff to drop their car keys through the letterbox when they dropped it off before the centre opened.
Kwik-Fit told the Kent and Sussex Courier newspaper its procedures were under review.
Mr Davey, of Hopgarden Road, parked his black Vauxhall Vectra in the garage car park at 6.30am and dropped the keys through a box, as he had been instructed to do by staff.