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There are several conversion tools available. Most tags for these tools would go in the head tags on your template. That is the easiest way to get them on every page while only having to add the code once. If you are asking which tool to use, that is the tricky part. Google Analytics has their ECommerce section in Beta right now, but that's what I use to manage my organic conversions. You can track transactions that happen on your site alone. Not phone calls or personal interactions unfortunately. If that tool ever develops, please let me know! GA is a free tool, and it is very accurate. If you haven't looked into that yet, I would check it out.