Measurement Protocol hits without cId

Question

I'm tracking my eCommerce site with Google Analytics and I'm using Googles Measurement Protocol to track offline payments. When a order is made, I save the client id from the cookie with the order. If a customer has something to prevent tracking, I still want to track the eCommerce purchase.

What cId should I set for those customers?

Answer 1

You can set any arbitrary number of string as client id and the tracking will report hits. But of course an arbitrary client id might not be usable to aggregate hits into sessions, an will not connect the hits from the measurement protocol to the hits from the web session (so you will lose the traffic source among other things).

Also the Google Analytics TOS state that you must not circumvent privacy features like e.g. an opt-out, so this might violate the terms of service.