Agency Guide: How to Set Up and Track Conversions for Google Ads Clients?

Trying to build up some confidence for next job.

But never had experience with setting tracking up with clients.

How is this usually done? Would they need a third party tool to capture GCLIDs etc?

Thanks

The short answer is:

How are GCLIDs and other essential IDs usually captured for client tracking?

Agencies track conversions and capture Google Click IDs (gclid) for clients primarily by implementing first-party tracking using Google Tag Manager (GTM) to read and persistently store the gclid from the landing page URL into a cookie, which is then sent to a server-side environment like Stape or Google Cloud Platform, or used on the client-side to fire conversion events.

The most robust and accurate method for capturing high-value offline conversions is using the Google Ads API to receive the stored gclid along with the conversion details from the server, which entirely eliminates reliance on third-party cookies or browser-side tracking failures.

The long answer is:

As an agency, setting up conversion tracking and ensuring you capture the gclid is one of the most critical and complex parts of your job, but it is entirely manageable and doesn’t always require a proprietary third-party tool.

The best practice method for agencies involves a three-stage approach focused on resilience and data ownership.

The first stage is Client-Side Capture using Google Tag Manager.

You install a custom GTM script on the client’s website that is specifically designed to read the gclid from the landing page URL when Google Ads auto-tagging is active.

This script then immediately stores the gclid into a first-party cookie or local storage, tying that unique ad click identifier to the user’s browser for up to the typical 90-day lookback window.

The second stage is Conversion Event Firing.

For typical website conversions, like a form submission or a button click, GTM simply reads the stored gclid from the cookie and sends it along as a parameter with the GA4 purchase or generate_lead event.

However, for the most challenging conversions, which are offline conversions (e.g., a sale that happens in a CRM 30 days later), the third stage, which is the Server-Side Solution, is essential.

Here, when the conversion occurs in the client’s Customer Relationship Management (CRM) system, your server-side environment (built on Stape or Google Cloud Platform) retrieves the original gclid associated with that customer.

You then use the Google Ads API to send the conversion details – including the gclid, the conversion time, and the conversion value—directly to Google Ads.

This is known as an Offline Conversion Import.

This system is superior because the conversion is recorded on your client’s server, making it immune to client-side issues like ad blockers, browser restrictions, and cross-device usage challenges.

By combining GTM for initial capture and the Google Ads API for reliable server-side reporting, you give the client the confidence that every conversion is being accurately measured and attributed for correct bidding optimization.

About The Author

Nabil El Alaoui Sossey

I’m Nabil, a marketing specialist from Sweden with 7+ years of experience helping e-commerce businesses improve their conversion tracking, attribution, and advertising performance.

I focus on implementing advanced solutions such as Facebook Conversions API, Google Ads API, Google Tag Manager, and Stape for Shopify, WooCommerce, HubSpot and other platforms.

My goal is to help brands move beyond basic pixel tracking to accurate, privacy-resilient data pipelines that power better optimization and more profitable campaigns.

Always happy to connect with business owners who want to take their tracking, ads, and growth strategy to the next level.

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