The art of selling vacuum cleaners has changed dramatically in recent years, as we discovered a few weeks ago. The two basic points today's vacuum cleaner salesperson has to put across quite categorically are a) that they are not selling anything and b) the thing they are not selling is definitely not a vacuum cleaner.

We were having a pleasant chat with some visitors one evening when Trish answered two phone calls within minutes of each other. After the second, her mildly amused expression aroused the curiosity of the rest of us. The first call, she explained, was from somebody who said we had been selected to receive a free silver-plated cake server. This was pretty exciting news, in view of the vast quantities of cake we serve on a daily basis. But this particular cake server had to be delivered personally and required an appointment at a time when we would both be home.

The second call had been from a close friend, warning us that we might receive a call from someone saying that we had been selected to receive a free silver-plated cake server. In order to receive theirs, he and his partner had sat through a vacuum cleaner demonstration nearly two hours long. At the end, the saleswoman had given them some sob story about not being paid unless she was given the names of more prospective customers. He was now phoning all his friends to apologise. Alas, he was just too late. We were to receive our cake server at 8pm on Thursday.

One of our visitors had heard of this routine before. She explained that they would tell us this appliance was not a vacuum cleaner at all but, in fact, an air purifier. It also cost $3000.

Over dinner on Thursday, we planned what we were going to say. It would be two against one, so we felt reasonably confident. I almost started tidying the lounge but Trish told me to leave it, as its existing condition limited the seating.

At 8pm precisely, a knock came on the door. A small Asian woman stood on the doorstep, empty-handed, maintaining a professional smile. She came in and sat in the only remaining free seat in the lounge. Trish sat opposite, restringing her guitar - a stroke of psychological genius, as it's a 12-string.

"So you're musicians?" the woman asked, glancing around at the mess. We could read her thoughts as the equation appeared in her mind: Musicians = No money.

"Are you here to sell something?" Trish asked. "Only we're not really in the market for anything right now."

She was here to tell us about a wonderful new air purifier. We sped things along by asking appropriate questions. Was it like a dehumidifier? No, it was much more than that. Did our friends buy one? No, but they were very impressed. Would the demonstration take more than ten minutes? Er, yes. We mentioned an impending band practice. Actually, it was taking place the following night but we neglected to make that clear.

Finally realising she would not achieve a demonstration here, let alone a sale, she began a new tack. Did we have any friends in the neighbourhood who might like to hear about this air purifier? We declined to give out the names of our neighbours.

"But you're my last call," she pleaded. "I have nowhere else to go."

"You could always go home," I suggested helpfully.

Eventually, she gave in, thanked us for our time and said if we're ever interested, just to give her a call. Except she left no business card or contact details. And, we realised as her tail-lights disappeared down the street, no cake server.