Smart contract for simulating an escrow

Escrow.sol

pragma solidity ^0.4.18;

contract Escrow {
    
    enum State {AWAITING_PAYMENT, AWAITING_DELIVERY, COMPLETE, REFUNDED}
    
    modifier buyerOnly() {
        require(msg.sender == buyer);
        _;
    }
    
    modifier inState(State expectedState) {
        require(currentState == expectedState);
        _;
    }
    
    State public currentState;
    
    address public buyer;
    address public seller;
    address public arbiter;
    
    function Escrow(address _buyer, address _seller, address _arbiter) {
        buyer = _buyer;
        seller = _seller;
        arbiter = _arbiter;
    }
    
    function sendPayment() buyerOnly inState(State.AWAITING_PAYMENT) payable {
        currentState = State.AWAITING_DELIVERY;
    }
    
    function confirmDelivery() buyerOnly inState(State.AWAITING_DELIVERY){
        currentState = State.COMPLETE;
        seller.send(this.balance);
    }
    
    function refundBuyer() inState(State.AWAITING_DELIVERY){
        require(msg.sender == arbiter);
        currentState = State.REFUNDED;
        buyer.send(this.balance);
    }
}