Get a list of installed chrome extensions

Go to chrome://system and click the expand button to the right of the "extensions" row. This provides a comma sorted list of all extensions. You can drag and highlight the list to copy.

This also has the benefit in that it lists on active extensions since installed but deactivated extensions can be ruled out. For a complete list have them activate all extensions they have, refresh the chrome://system page and copy the now updated list.

Is there an easy way for the user to provide me with a list of installed extensions?

You can use BrowserAddonsView from Nirsoft:

BrowserAddonsView is a simple tool that displays the details of all Web browser addons/plugins installed in your system. BrowserAddonsView can scan and detect the addons of most popular Web browsers: Chrome, Firefox, and Internet Explorer. For Chrome and Firefox, BrowserAddonsView detects and scans all Web browser profiles if there are multiple profiles.

Your can sort the output by "Web Browser" and then select the Chrome extensions.

Then either:

1. "File" > "Save Selected Items" to export to a text file, or

2. "View" > "HTML Report - Selected Items"

Here is an extract from the text file for my Chrome:

> type extensions.txt
==================================================
Item ID           : cfhdojbkjhnklbpkdaibdccddilifddb
Status            : Enabled
Web Browser       : Chrome
Addon Type        : Extension
Name              : Adblock Plus
Version           : 1.12.4
Description       : Used by over 50 million people, a free ad blocker that blocks ALL annoying ads, malware and tracking.
Title             : Adblock Plus
Creator           :
Install Time      : 10/11/2016 11:20:33
Update Time       :
Homepage URL      :
Update URL        : https://clients2.google.com/service/update2/crx
Source URL        :
Addon Filename    : C:\Users\DavidPostill\AppData\Local\Google\Chrome\User Data\Default\Extensions\cfhdojbkjhnklbpkdaibdccddilifddb\1.12.4_0\manifest.json
Addon File Created Time: 10/11/2016 11:20:31
Addon File Modified Time: 10/11/2016 11:20:32
Size              :
Profile Folder    : C:\Users\DavidPostill\AppData\Local\Google\Chrome\User Data\Default
==================================================

The user can email you this text file.

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Disclaimer

I am not affiliated with Nirsoft in any way, I am just an end user of their software.