My father died earlier this year and I have been trying to sell his car through small ads with little success. At the start of November, I received a cold call from Car Data (cardata.co.uk). It said it had "a number of buyers desperate for a car like yours". I said I didn't want to spend any more money advertising but I was persuaded to part with £99.50 that would be reimbursed once my car was sold in a matter of days. It has not been sold and I want to highlight this practice. RW, north London

Car-matching schemes like this rely on the desperation of consumers to sell to encourage the payment of an upfront fee. It's interesting that the credit card fee is set at £99.50, which is just below the threshold where you could get a refund from your credit card company if, or when, Car Data promises fail to materialise. It was reluctant to answer questions and refuses to offer a refund. Anyone selling a car is highly likely to get a call from Car Data, or a similar operator. The simple advice is: never agree to payment of an upfront fee.

Answering your letters this week is Steve Playle, Trading Standards officer and Team Leader at Surrey Trading Standards Service.

We welcome letters but regret we cannot answer individually. Email: capital.letters@theguardian.com. Please include a daytime phone number.