I've just got back from a quote to find a message from a customer asking for a refund. Apparently the online booking system took double payments.
The problem was that we don't do online booking and he had not booked with us.
I phoned him back and he said he could not remember who he had booked with as it was through Groupon!
He looked for them on Google and saw our site and assumed it was us. I asked him who was doing the Groupon ads but he could not remember (then his phone went dead).