Juan Muñoz at Tate Modern

A visit to the late Juan Muñoz’s retrospective at Tate Modern (until 27 April) is not a relaxing thing, and yet singularly memorable. There is the continual feeling that one is an uninvited guest, and that you’ve come in the wrong door and are seeing everything from the wrong angle. Backs are turned towards us, figures group in an excluding way.

In The Prompter, 1988, the back of a dwarf is visible in a prompter’s box at the front of an empty stage – but try as we might we can’t see its face, and there is no prompting, and no sound. A drum is propped against a wall at the back of the stage. It’s hard to know how to react, but by then we have already reacted – by feeling kept at bay and excluded.

In Staring at the Sea, 1997-2000, two standing figures look at their reflections in a mirror, but their faces are covered by cardboard masks. They each look like the other, and there is little to be gained by them looking in the mirror. Whichever way you look at it, it seems like the back.

Many Times, 1999, in Room 10 is filled with 100 figures representing a single Asian man modelled on an art nouveau ceramic bust Muñoz came upon in a hotel. The manically smiling figures gather in groups, conversing and laughing, but they are smaller than lifesize so that visitors meandering among them stand head and shoulders above their heads. We are the ones that are left exposed and unusual rather than them.

This show is a matter of reflections, shadows, light and theatre – and a sense of unease – rather than a sculptural event. They are powerful images, but hard to endure. The spotlight illuminating Shadow and Mouth, 1996, of two figures in a strong beam, has blown out, smashing its glass, according to the attendant. A makeshift replacement spotlight stands alongside it, picking out the few remaining uncollected shards in its beam. Even the lighting finds it hard to take.

Are you being conned?

I have details about how to buy my works on my website and get interest from buyers from time to time, but getting two interested buyers ready to send me hundreds of pounds in one week without another question was always going to seem suspicious.

One email was by someone claiming to be a priest wanting to buy several works as a present for his parents on their 50th wedding anniversary, the other by a man wanting a wedding present for a friend. What made them stand out was their willingness to part with hundreds of pounds at the earliest possible opportunity, their poor grasp of the English language and a writing style that suggested they were ordering 15,000 ball-bearings rather that a piece of art.

Websites are a great first point of contact for potential buyers of work from unrepresented artists, but they don’t usually lead to mass orders and untold riches. So the appeal of such unquestioning enthusiasm to own one’s work is understandable – someone really likes my work and wants to buy some. It’s what you hope for from your website when you first get it set up – orders rolling in each week – but it doesn’t usually happen quite like that.

The style of email is instantly familiar. The writer is certainly a close relative of, if not the very same, person who wrote to me the week before to generously give me the chance of sharing the $10 million his father, the owner of a large oil company, left to him after his sudden death in Ivory Coast last year. Touched as I was by this kind gesture, it was an opportunity, like many other similar opportunities, I let pass.

I was suspicious, but curious too, about these people interested in buying my prints. The priest wanted to know the total cost of the list of works he was ordering. I asked for his address and phone number first. He lives, he claims, a couple of miles down the road from here, on the edge of London’s financial district, and can send a courier around to pick the works up without me having to pack them and pass on postal charges. The phone number he gives is nonsensical and obviously fake. Even though I would only accept payment by Paypal, and don't know quite how I would end up being out of pocket, I let it drop. There are better things to do.

Other artist acquaintances have had similar recent emails from people wanting to buy work in this way. How many artists have been conned like this already? How many have had their egos massaged enough to let the conmen slip beneath their radar? Anyone with an email address is accustomed to questioning the validity of what lands in their inbox each day, even if it doesn’t end up their junk box first. But if these scam emails are being sent out, and increasingly so, there must be at least a few artists who are losing out, somehow, because of them.