We monitor nothing, and we do not keep track of our users. Like most of the apps and sites do, we too use analytic libraries, but we do that only to get an estimation of the number of users who are using this app.
The GPS is on only when you use the app, and it is used to find your location and download the sales that are available in your country. We store no information about your location in our server.
When you post a sale, we do store your location, but this is not your location per se, but the location of the store that you are writing the sale about.