Web tracking for an advertising site?

Question

Internet advertising

Can you suggest? there is a site to which clients come from another site. The question is next. How expensive and problematic it is to install on a site that makes a sale a software "gadget" showing what actions the client did on this site (ordered, registered, consulted online) coming from another site on which he initially saw an advertisement about them. And is it possible to protect such data from changes by the owner of the selling site (who has this gadget we install) How will this price depend on the CMS on the selling site or is it not important?

Answer 1

set up Google Analytics and set up reports so that you can see it
sometimes, when they can’t set it up so that it doesn’t show you inappropriate information, they use the GA API

Answer 2

Installing Google Analytics and Yandex. Metrics.
You can set goals in it (detailed description is in the help). You can configure it both with the help of scripts and by the usual sorting by target pages (but scripts are more reliable).
Click, scroll and webvisor maps (visit records) are available in Yandex. Metrica.