function payEther(uint transactionId) {
      
      if(transactionId < 1 || transactionId >= transactions.length) { throw; }

      
      uint etherPaid = msg.value;
      uint etherAskedFor = transactions[transactionId].amount;
      uint etherNeeded = etherAskedFor + transactionFee;

      
      if(etherPaid < etherNeeded) { throw; }

      
      uint payback = etherPaid - etherNeeded;
      
      msg.sender.send(payback);

      
      sellers[transactions[transactionId].sellerId].etherAddress.send(etherAskedFor);
      
      sellers[transactions[transactionId].sellerId].transactionsPaid += 1;

      
      

      
      transactions[transactionId].paid = true;
      
      transactions[transactionId].paidWithAddress = msg.sender;
    
      
    }