RhinoFish - 9:00 pm on Jan 31, 2013 (gmt 0)
are you using the AdWords Conversion Tracking script -or- importing Analytics Ecommerce or goals?
do you place conditional parameters on the script, like session active?
do you use PayPal which can break tracking in several ways?
if you're doing testing, are you switching to a new browser or making sure there's a fresh click, so the conversion is a 1-per and not a many-per?
there's some reporting delay, it varies some, it's very different when using an AdWords script (~several hours), as compared to importing conversion data from Analytics (sometimes days)?
AdWords records sale on date of click, Analytics on date of sale... are you allowing for this?
in the AdWords conversion module, have you inspected the URLs posting the sales data, see if there's anything up with what is reporting, or missing from pages that are reporting?
are you making sure to stick to https (or not)?
did you make sure you don't have any parameters being appended that might be interfering with your scripting?
are you advertising on mobile, and using a mobile version of the script there?
set up a URL goal in Analytics, have it also track loads of that page, see if that assists your sleuthing.
order the scripts on the receipt page by importance, is AdW and Analytics Ecom high on the page?
do you have too many 3rd party scripts, or ones from shady partners, on the page (especially before the AdW script)?
are you using a conditional include, look for that?
there's more... but i'm tired already.