Like many websites, my customer's website is advertising funded. A number of customers pay to have advert images on their website. However a couple of times now, the advert customers have noticed that the stats we're giving them for outbound clicks do not tally up with the number of inbound referrals they see in Google Analytics (even though the URL is tagged with the google UTM information.
The figures are out by around 5 times, so it's not like this is a small discrepancy. If we track someone clicking an outbound advert link on our site (via a click-tracker URL) then only about 1 in 5 of those will show up in Google Analytics. Yet if I test it myself with a browser, I seem to see ALL the click throughs register on the advertiser's site in the "real time" view.
As an example, our site tracked 100 outbound clicks to the advertisers site last month, but their Analytics stats only recorded 20 against the campaign URL, while the number of "referrals" was 0 (so even when the campaign URL WAS tracked, Google didn't seem to notice which site it had come from). Do browsers not send referrer information any more?
I've blocked the adclick URL using robots.txt to limit robots inflating the outbound clicks but I realise they might not obey this file.
What could be causing this large discrepancy? Are there any additional logs I should collect in my click tracker which might help diagnose this? eg, IP address or user-agent?
I might be misunderstanding you, but if your links are tagged with utm parameters they will not show up as referrals. Instead they will show up with whatever you have set as utm_source, so you should look into the "All Traffic" report and see if you can find your parameter name there.