Operating multiple domains that offer exact or somewhat similar products requires detailed monitoring. You might wish to monitor and manage conversions across multiple domains so as to optimize your marketing strategy.
You will need to monitor and measure cross-domain clicks so as to allocate end revenue numbers for each touch point on your various domains. You can correspondingly modify your marketing strategy based on those figures. For instance, you could have 3 or 4 websites that sell same or similar products, but use a different approach and pricing strategy, and could be positioned differently based on specific marketing campaign strategy for each website.
You would wish to study cross product as well as cross domain sales and patterns to understand client preferences and behavior with regard to several products on different domains. If you plan to use Google AdWords to track such conversions then you will not be able to monitor client behavior over different domains although cross-campaign, ad group, and keyword data reports can be extracted.
On the other hand, if you have used a single AdWords account for all your domains then you will be able to monitor and measure transition paths across all your domains. However, monitoring conversions still possesses a challenge due to various reasons. One hurdle in this path is the fact that your clients might use desktops or mobiles or tablets to access your multiple domains and using tracking based on cookies will be tough since each device and browser uses different and specific cookies.
Again, if your clients use the same browser, then it is still difficult to measure conversions across your multiple domains since each of your websites too would possess unique cookies. You will certainly need advanced skills to monitor and measure conversions by multiple websites and devices.
Even Google Analytics has limited capabilities to measure cross conversions including measuring through cross channel transition paths and you would anyway need to tag your marketing campaign to use this feature. You will also not be able to specifically measure each touch point or even adjust bids using the manual or automatic option.
You will need a solution that offers greater insight into revenues coming in from multiple domains so as to modify your marketing strategy accordingly. Such solutions are available and you can use them to monitor and measure cross conversions across multiple domains to optimize your campaign for all required websites.