Imagine turning up with a reputable estate agent to view a property to rent - only to find a tenant already in the bath, and realise the place has already been let. In other cases, people interested in renting can make a long journey to look at a property, only to find they have already been shown it.

These sort of incidents have been happening in the residential lettings market lately - thanks to a trend by landlords to put their properties on the books of multiple estate agents, in response to an over-supply of properties in the market. Landlords want to get maximum coverage for a property since time is money and they don't want empty spaces. "We have had cases of people arriving on a doorstep only to announce that they have already been shown the property by a different agent," says Brid O'Sullivan, a director of Christies. "It wastes everyone's time and people coming from abroad find it especially hard to handle. They think the system is mad."

Naturally, agents aren't happy with landlords multiple listing their properties, and are seeking ways to avoid confusion. There are now over 12 major letting agents in the market, compared to around three in 1991.

The attempt to maximise coverage is to the long-term disadvantage of landlords, says id O'Sullivan. "The professionalism is being taken away from the agent with this change in the way properties are listed. Sometimes there are different prices on different lists. A landlord will change the price with one agent and not bother to contact the other agents and so it leads to total confusion."

However, the Irish Auctioneers and Valuers Institute (IAVI) is reluctant to have formal arrangements. "We would be against over-regulation because of the fluctuations in the property market," says the organisation's president, Wendy-Jane Catherwood "Circumstances do change. It depends on market conditions. It is up to agents and landlords to come to an agreement about particular properties."

She also points out that some letting agents just charge a fee to the prospective tenant, who is then shown a list and the landlord is charged nothing for the facility.

Christies, however, offers the full service of showing the property and organising the lease and acts as the middleman between the tenant and landlord. They have been operating in the market since 1991.

It is landlords who are missing out in the long-term, says Brid O'Sullivan and she appeals to them - and to the agents themselves - not to go along with multiple lettings until a property has been on the market for a time. "Agents are now realising that landlords are listing their properties all over the place and we will not give priority to those properties." Ms O'Sullivan id worked for some years in the residential letting market in London where agents have worked out a system among themselves. "Multiple listing is popular in London, but there is a 10 per cent letting fee to be divided up. Here the rate is generally six to seven per cent, or even five to seven per cent. Some agents quote as low as four per cent." The present system is certainly confusing for the client, especially since the agents don't give out the actual number of the property being rented. This is traditional and is generally done so as not to alert burglars to an empty house.

The other problem with listing numbers was that other agents could approach the landlord and poach you - but now the landlords are the ones calling the shots. The solution, says O'Sullivan, is some form of compromise. She says agents would like to see a situation where one company would have sole agency on a property for three or four weeks. They would try to let the property within that time but after that, an agent would be free to negotiate to share it with another agency.

But Wendy-Jane Catherwood says it is up to the landlord to come to an agreement with a particular agent. "Agents advise clients on the best method of selling or letting a property, but it is up to the client to decide on the options," she says.

She agrees that having sole agency on a property is attractive from the agent's point of view when a market is sluggish, but she says they can "fall between two stools. In theory, it's a great idea, but in practice it doesn't seem to work." But Sherry FitzGerald has adopted the policy of accepting only properties giving the firm sole agency of a given property for a month. David Lewis, who heads up the residential letting division, says: "We put an awful lot of work into each letting. We show the properties ourselves and we're confident that if we've done a reasonable job, we'll have results."

He says it isn't doing the landlords any favours. "They want to have five times the amount of work being done for one fee," he says. "That's out of all proportion. Anyway, it smacks of desperation from their point of view. It doesn't do the properties any good with potential tenants turning up to the different agents and seeing the same property on all the books."

Sherry FitzGerald has only been involved in the residential letting business since the beginning of this year. "We wanted to provide an all-round service," says David Lewis. "We get a lot of business selling properties to investors who then ask us if we have a lettings department."

Indeed, also part of this trend to expand is Christies, which has also moved into selling as well as letting properties. It is unusual for joint agents to be involved in selling a property in the city. It sometimes happens out of town, or when a particularly big property is involved.

"None of the larger agents would tolerate that sort of multiple listings in sales," says David Lewis. "There's no reason to do it in lettings either."

Some agents work harder than other agents and landlords would certainly have more bargaining power if they gave the property to just one agent.

Carina Warner, of the residential lettings division of Hooke and MacDonald, isn't surprised the agents are angry. She also agrees with the logic of agents having a property to let exclusively for a month before a free-for-all develops. She points out, however, that a month can be a long time at certain times of the year, or a short time when things are quiet. "May would generally be a quiet time, although it is busier than last year," she says.

She has also run into problems with the multiple lettings system. "You might ring up to say you have a tenant for an apartment only to be told the apartment has been let. You get back to the tenant with the bad news and then they're upset. But then the letting can fall through and the landlord gets back to you but by then the tenant is gone."