After creating a new screenshot in PagePixels, set how often you'd like it to take this screenshot. Once a day should suffice for customer review services. This also means you won't breach the 100 screenshots per month offered by the free plan.
Paste the URL you'd like to capture. For Trustpilot and Google this is your URL where your businesses' ratings appear.
By default, a screenshot of the entire window is taken, but you can provide a CSS selector to screenshot only a specific part of the page. Inspect the code in your browser to find the CSS selector you need. The example below is from Trustpilot.
When you've finished configuring your screenshot, save it. This will generate the share URL and take the first screenshot.
From the gallery, click the gear icon beside your image. Click Share URL and copy it.
Return to your Geckoboard dashboard and add a new Image widget.
Paste the copied URL to the URL field, set a Reload duration, then click Save widget. Your image will now appear on your dashboard.