diff --git a/Sources/AppStoreConnectCLI/Commands/TestFlight/Sync/TestFlightProgramDifference.swift b/Sources/AppStoreConnectCLI/Commands/TestFlight/Sync/TestFlightProgramDifference.swift
index e63e2682..3a96883f 100644
--- a/Sources/AppStoreConnectCLI/Commands/TestFlight/Sync/TestFlightProgramDifference.swift
+++ b/Sources/AppStoreConnectCLI/Commands/TestFlight/Sync/TestFlightProgramDifference.swift
@@ -52,9 +52,20 @@ struct TestFlightProgramDifference {
         }
     }
 
+    enum Error: LocalizedError, Equatable {
+        case duplicateTesters(email: String)
+
+        var errorDescription: String? {
+            switch self {
+            case .duplicateTesters(let email):
+                return "There are two beta testers with the same email '\(email)' exists in your account, please clean that up before continue."
+            }
+        }
+    }
+
     let changes: [Change]
 
-    init(local: TestFlightProgram, remote: TestFlightProgram) {
+    init(local: TestFlightProgram, remote: TestFlightProgram) throws {
         var changes: [Change] = []
 
         // Groups
@@ -80,6 +91,10 @@ struct TestFlightProgramDifference {
             let remoteApps = remoteTester.apps
             let remoteBetaGroups = remoteTester.betaGroups
 
+            if remote.testers.filter({ $0.email == remoteTester.email}).count > 1 {
+                throw Error.duplicateTesters(email: remoteTester.email ?? "")
+            }
+
             if let localTester = local.testers.first(where: { $0.email == remoteTester.email }) {
                 let appsToAdd = localTester.apps.filter { app in
                     let appIds = remoteApps.map(\.id) + remoteBetaGroups.compactMap(\.app?.id)
diff --git a/Sources/AppStoreConnectCLI/Commands/TestFlight/Sync/TestFlightPushCommand.swift b/Sources/AppStoreConnectCLI/Commands/TestFlight/Sync/TestFlightPushCommand.swift
index d336c110..50ecea9e 100644
--- a/Sources/AppStoreConnectCLI/Commands/TestFlight/Sync/TestFlightPushCommand.swift
+++ b/Sources/AppStoreConnectCLI/Commands/TestFlight/Sync/TestFlightPushCommand.swift
@@ -26,7 +26,7 @@ struct TestFlightPushCommand: CommonParsableCommand {
         let local = try FileSystem.readTestFlightConfiguration(from: inputPath)
         let remote = try service.getTestFlightProgram()
 
-        let difference = TestFlightProgramDifference(local: local, remote: remote)
+        let difference = try TestFlightProgramDifference(local: local, remote: remote)
 
         difference.changes.forEach { print($0.description) }
 
diff --git a/Sources/FileSystem/Configuration/TestFlightConfigurationProcessor.swift b/Sources/FileSystem/Configuration/TestFlightConfigurationProcessor.swift
index d52d39f4..fbc7f1c3 100644
--- a/Sources/FileSystem/Configuration/TestFlightConfigurationProcessor.swift
+++ b/Sources/FileSystem/Configuration/TestFlightConfigurationProcessor.swift
@@ -60,18 +60,25 @@ struct TestFlightConfigurationProcessor {
 
     enum Error: LocalizedError {
         case testerNotInTestersList(email: String, betaGroup: BetaGroup, app: App)
+        case noValidApp
 
         var errorDescription: String? {
             switch self {
             case .testerNotInTestersList(let email, let betaGroup, let app):
                 return "Tester with email: \(email) in beta group named: \(betaGroup.groupName) " +
                     "for app: \(app.bundleId) is not included in the \(betaTestersCSVName) file"
+
+            case .noValidApp:
+                return "There's no valid app folder found in your local configuration file path, please run 'sync pull' first"
             }
         }
     }
 
     func readConfiguration() throws -> TestFlightConfiguration {
         let folder = try Folder(path: path)
+
+        guard folder.subfolders.count() > 0 else { throw Error.noValidApp }
+
         var configuration = TestFlightConfiguration()
 
         let decodeBetaTesters: (Data) throws -> [BetaTester] = { data in
diff --git a/Tests/appstoreconnect-cliTests/Sync/TestFlightProgramDifferenceTests.swift b/Tests/appstoreconnect-cliTests/Sync/TestFlightProgramDifferenceTests.swift
new file mode 100644
index 00000000..bd0c70aa
--- /dev/null
+++ b/Tests/appstoreconnect-cliTests/Sync/TestFlightProgramDifferenceTests.swift
@@ -0,0 +1,54 @@
+// Copyright 2020 Itty Bitty Apps Pty Ltd
+
+@testable import AppStoreConnectCLI
+
+import FileSystem
+import Model
+import Foundation
+import XCTest
+
+final class TestFlightProgramDifferenceTests: XCTestCase {
+
+    func testErrorWillBeThrow_whenDuplicateTesters() throws {
+        let local = TestFlightProgram(
+            apps: [],
+            testers: [BetaTester(email: "foo@gmail.com", firstName: "Foo", lastName: "Bar", inviteType: "EMAIL", betaGroups: [], apps: [])],
+            groups: []
+        )
+
+        let remote = TestFlightProgram(
+            apps: [],
+            testers: [
+                BetaTester(email: "foo@gmail.com", firstName: "Foo", lastName: "Bar", inviteType: "EMAIL", betaGroups: [], apps: []),
+                BetaTester(email: "foo@gmail.com", firstName: "Foo", lastName: "Bar", inviteType: "EMAIL", betaGroups: [], apps: []),
+            ],
+            groups: []
+        )
+
+        XCTAssertThrowsError(try TestFlightProgramDifference(local: local, remote: remote)) { error in
+            XCTAssertEqual(
+                error as? TestFlightProgramDifference.Error,
+                TestFlightProgramDifference.Error.duplicateTesters(email: "foo@gmail.com")
+            )
+        }
+    }
+
+    func testErrorNotThrow_withoutDuplicateTesters() throws {
+        let local = TestFlightProgram(
+            apps: [],
+            testers: [BetaTester(email: "foo@gmail.com", firstName: "Foo", lastName: "Bar", inviteType: "EMAIL", betaGroups: [], apps: [])],
+            groups: []
+        )
+
+        let remote = TestFlightProgram(
+            apps: [],
+            testers: [BetaTester(email: "foo@gmail.com", firstName: "Foo", lastName: "Bar", inviteType: "EMAIL", betaGroups: [], apps: [])],
+            groups: []
+        )
+
+        let result = try TestFlightProgramDifference(local: local, remote: remote)
+
+        XCTAssertTrue(result.changes.isEmpty)
+    }
+
+}