client/lib/purchases/index.js
function isCancelable( purchase ) {
	if ( isIncludedWithPlan( purchase ) ) {
		return false;
	}

	if ( isPendingTransfer( purchase ) ) {
		return false;
	}

	if ( isExpired( purchase ) ) {
		return false;
	}

	if ( isRefundable( purchase ) ) {
		return true;
	}

	return purchase.canDisableAutoRenew;
}
function isCancelable( purchase ) {
	if ( isIncludedWithPlan( purchase ) ) {
		return false;
	}

	if ( isPendingTransfer( purchase ) ) {
		return false;
	}

	if ( isExpired( purchase ) ) {
		return false;
	}

	if ( isRefundable( purchase ) ) {
		return true;
	}

	return purchase.canDisableAutoRenew;
}
Checks if a purchase can be cancelled.
Returns true for purchases that aren't expired
Also returns true for purchases whether or not they are after the refund period.
Purchases included with a plan can't be cancelled.

@param {Object} purchase - the purchase with which we are concerned
@return {boolean} whether the purchase is cancelable