Ashley and Luke Norman, who run Lawn Enforcers, had £1,000 worth of equipment stolen from their van at the Bilston branch of B&Q on Thursday.
The theft included a mower, two strimmers and a post hole borer.
The pair parked in in the area where tradesmen load their goods, but when they entered the store to pay for their supplies, the thieves struck.
As there was no CCTV coverage in the trade section of the car park, police told the pair that there was little they can do.
Ashley, 29, from Coseley, said: “I parked in the trade section.
“While I was inside, the stuff was taken. I just want to make people aware.