OpenCart Help: Set Up Google Base Product Feed in Merchant Center
I am adding this tutorial because I have not seen this process explained adequately anywhere else.
Setting up a google base products feed in Open Cart is easy. Just go to Extensions/Product Feeds, install Google Base, then edit it and select 'enable.' Copy the url of the feed given there because you will need it for the Google Merchant Center, which is the real trick of this set up.
First off, Google will reject your feed if you don't have a manufacturer and an mpn (or the international equivalent) for each product. If you are a crafter, artist, etc., it's not obvious in OpenCart that you need to add yourself as a manufacturer, but you do for Google. So go to Catalog/Manufacturers and add your business name there. Then each time you add a product that you make, you must add yourself as the manufacturer on the Links tab. If you are a small business you probably don't have an mpn for each item. No problem, just copy your Model number to the MPN field on the Data tab each time you add a product. Those are the hoops you have to jump through for Google. If you're like us, then you don't realize this until you've added a lot of products, and the prospect of going back through each one is not a happy one.
If you know what you're doing, you can make mass changes by editing the opencart database for your site. To do this first add yourself as a manufacturer, then edit one product through the OpenCart admin panel, add your manufacturer name to that product, and save it. Then through your webhost's cpanel find your way to your opencart database. Navigate to the 'products' table. First, backup that table by exporting it as sql. Then export it as csv. You can edit the csv file on your computer with Gnumeric or OpenOffice or any spreadsheet program. Copy all the data from the model column to the mpn column, and set all the numbers in the manufacturer column to the number of the item you added (all the other items will be '0'). Be sure to save the file as csv. Double-check your work, then import that edited csv file back into your products table selecting the overwrite option. If you messed something up, then import the sql backup file with overwrite option. Ask for help if you are unsure about editing your database!
Now you are ready to sign up for the Google Merchant Center here: http://www.google.com/merchants/signup. The sign-up process is fairly self-explanatory, except to you will have to verify that you are the owner of your url. Google will give you a file to upload to your site in order to do that (if you don't know how to FTP to your site, get someone to help you). After you upload that file, make sure you click the 'verify' link on the General Settings page (Settings/General). Also fill in the other information on that page, and click 'save.' But there's more: Google will also reject your feed if you don't have a shipping method and a tax method. Your feed will not supply those, so you have to set that up under Settings/Tax and Shipping. Once you find your way there, it is self-explanatory.
Now, you are finally ready to add you feed to the Merchant Center. Go to the Data Feeds page, click 'add new,' and enter the filename of your feed, which is just the very last part of that url you copied from OpenCart (google_base). They just want the file name here, not the whole url. Once you've added that feed, you can click on the 'schedule upload' link under the Upload column. This is where you enter the whole url. Click 'schedule' and you're done! Be sure to check back in at the Merchant Center the next day for possible errors.