For a few, though, pictures are not enough. They contact the agents and present themselves as plausible buyers of expensive properties and then proceed to string everyone along until they can bluff no more. At this point, they usually disappear.
They are quite different from the numerous time-wasters who are merely curious about how the wealthy live or want a few good decorating ideas. Far from being satisfied with a quick snoop, their game is not over until, at the very least, their offer has been accepted.
David Forbes of Chesterfields has come across two such American operators recently. "One wanted to buy a pounds 3m house the other a pounds 5m property. They had very good stories about claiming to be in the media and in Hollywood. They both made offers and even instructed UK solicitors. One then disappeared while the other kept finding excuses for not producing a financial reference."
Not unnaturally, vendors left in the lurch take their frustrations out on the agents. "We cannot turn down someone who appears to be genuine," says Mr Forbes. "We do carry out checks, but there are limits. It is not the culture here to get financial references at this stage and most people would get pretty upset if you did ask. In parts of America you have to provide proof of wealth before you can look round a high-value home."
It is not surprising that David Forbes would like this to become the practice here. He has seen bogus buyers go as far as employing the staff of a large house, instructing solicitors and surveyors and then disappearing just before the exchange of contracts. One so-called buyer was only found out after he was overhead boasting about his deception in a Chelsea pub.
So why should anyone want to pretend to buy a house? According to Cary Cooper, professor of psychology at UMIST in Manchester, they are delusional either because they have convinced themselves they can buy or they have to save face by keeping going. "Such imposters have no self-worth," he says. "If they weren't buying houses they would be acting out other roles. At the voyeuristic level, they like going round, say, a movie star's house to put a bit of glamour into their lives."
Clearly, the attention paid to anyone who looks good for a few million is a great boost to the ego, and celebrity homes have the bogus buyers out in force. When Savills was selling David Lean's house in Docklands the company was strung along twice by bogus offers, despite numerous checks, recalls Jonathan Hewlett. Some owners require people to sign a confidentiality clause before looking around. "I always ask one or two pertinent questions. If the buyers are genuine they will answer you openly. Anyone rude or abrupt sets the alarm bells ringing." says Mr Hewlett.
It is not just the top end of the market that suffers from time-wasters. The boom in new-build absorbs a good share of the "carpet-treaders" whose idea of a good weekend is viewing someone's house, but there are those who are put in offers with no intention of buying or as a back-up while continuing to look around. Henry Woods of Douglas & Gordon's Battersea office recently took a couple with pounds 300,000 to spend around a number of four-bedroom houses. After two weeks of intensive negotiation a price was agreed. "They were moving from a nasty high-rise block so were excited about the whole affair. They had tea with the vendors and measured up and contracts were sent out. My suspicions were aroused when I kept seeing them around even though they were supposed to be abroad. They told us contracts and a banker's draft had been sent by registered post and we spent ages rooting around in the local sorting office. The couple then evaporated into thin air."
The fact that nothing locks buyers or sellers into a binding agreement until contracts are exchanged makes it ripe for exploitation. "Anyone can make any number of offers and legally we have to write to our clients with details. We will of course warn them if we have any doubts," says Mr Woods.
While agents can spot the more obvious fantasists - those who ask where they can park their McLaren F1, or those with an impressionable girlfriend in tow - they are aware of the possibility that they could be genuine. Jonathan Hewlett, weary of hearing about relatives who are princes or sultans, had his doubts about a very large bid. "I was told that the man had arrived in the country with a full police and diplomatic escort. He just seemed implausible to me." And David Forbes knows of one agent who must be rueing the day he ignored a scruffy young man wearing a baseball cap. "The man then went round the corner and spent pounds 4m."