I found this on a Cork based Eproperty website. Its a pretty good description of what you should expect if using two auctioneers. I can see big issues arising when it comes to deciding who found the buyer?
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Are two auctioneers better than one?
Choosing the right auctioneer will help take much of the stress out of selling your home. You want to find a professional, trustworthy, and energetic auctioneer who has a track record of selling homes in your area. The best way to do this is to ask friends, neighbours and colleagues who recently bought or sold their homes. They can refer you to the good auctioneers who operate in your area.
A joint agency is where you appoint two or more auctioneers to sell your home. They may agree to split the fee, or the full fee may go to the successful seller. Getting two for the price of one might sound like good value, but in most cases it is a mistake. Good auctioneers are busy, and you will get the best service when you commit to working exclusively with them. They concentrate most of their energy on the properties where they are the sole agents.
Some sellers mistakenly believe that their chances of a successful sale increase with each additional auctioneer they appoint. The good ones are often selective and will only work with buyers when they are the sole agents.
However, there are cases when joint agencies can work well. This often happens when the seller is trying to reach two distinct markets. For example, a country home may be targeted at both local and international buyers. In that case a joint agency between a local auctioneer and a larger firm with international contacts may be appropriate. But to get the most out of both auctioneers, and to increase the chances of a successful sale, the seller may have to commit to a higher fee to be split between both parties.