Unfortunately since most people use Adblock software of some kind which blocks those 1x1 pixel trackers or NoScript which blocks embedded scripting like GA with surrogates giving empty payloads or even Ghostery or Abine, the whole system is not going to reflect accurately what you need to know.
However, if you have access to your servers raw logs or have a way to get filtered reports, you can track how many times a special thank you image (only displayed on the confirmation page) has been accessed/loaded telling you how many people landed on that page which resulted in the resource being pulled. Its very similar to the 1x1 pixel method but with the distinct advantage that it will not get filtered due to its custom size.
You can also include in link tracking of usage in addition to GA so that you can make sure if the GA function is broken, you have an alternative. Such as
www.whatever.com/product.php?item=###&cid=hash_of_user_info (such as browser, OS, date, time, whatever you want to keep track of) and because they are passed in the URL, the server logs once again will have an actual link hit (similar to what Google started doing after noticing their GA was useless to them in most cases) and you can search the log for the unique CID and see what they saw and where they looked.