It can also get messy. For example, what is "the selling agent"? Say buyer A views the house with Agent A, but subsequently pays the deposit to Agent B. Under Irish law the first agent is the seller in this case as they introduced the buyer, however, Agent B has the deposit and will probably consider himself the seller.
This probably wouldn't happen, but never say never!
Even agreeing a 50/50 fee split may result in one agent sitting back and letting the othe do the work.