Two men in a white van offered to cut down a bush in the front garden before charging the owners £250 for 15 minutes work.
And one of the men then followed the resident into their house as they went to look for the money to pay, council chiefs said.
And when the resident didn't have enough money in their house, they were taken down to the bank so the men could be paid.
And they returned a couple of days later to remove the roots of the bush and charged the resident another £150 for the work.
Councillor Nicolas Barlow, cabinet member responsible for trading standards, said: "This incident must have been very upsetting for the people involved, and we do all we can to highlight these cases to protect others.
"I cannot stress enough how important it is to be vigilant and not buy goods or services over the doorstep. Reputable workers will not go door to door touting for business and will always give a customer a written quote. They should also outline the customer’s rights of cancellation for any work over the value of £42 before starting the work.
"And certainly, a reputable trader will never, ever follow people into their homes while they look for money or take a consumer to the bank to get money to pay them."
Any suspicious callers, going door-to-door, offering to carry out any sort of gardening or property maintenance should be reported immediately to the Bogus Caller Hotline on 01384 812045.