This has been mentioned a few times so far, the feed is uploading perfect with XX number of products, but it is only publishing a small percentage of them through Google.

This is usually, caused by one main reason....

Duplicate ID Numbers.
The feed is constructed by using the ID number, but if the product is added to child categories or 2 or more categories, then it will add that product in more than once so will have the same URL link, title and ID number. Even if the child category gives that product a different name, it will still cause problems, as the same ID number will be added more than once. Google will decline any products with duplicate ID Numbers

QUOTE:
http://groups.google.com/group/base-help-roadblocks/browse_thread/thread/8f1457dc19e293c6?fwc=1

Good Evening Basers!

We often receive emails from content providers who aren't able to find all of their items on Google Base. One common reason for this is the inclusion of duplicate "title" or "link" values in a bulk
upload. For example, items hosted on the same page will typically include the same URL in the "link" attribute. Sometimes, items will have the same "title" but different properties; perhaps the
item's color, size or storage capacity. It's natural that anyone submitting data to us would want all of these similar, yet slightly different items to appear.

To do so, you'll need to include our "ID" attribute. Providing a unique "ID" for every item is a good way to ensure that all of your items appear, even if some items share an item page or title. If you
are submitting your items for inclusion on both our US and UK properties, you'll need to use unique "ID" values in each of your two files. Formatting tips for the "ID" attribute are available
here:

The way the feed works with the Virtuemart system, is a little complicated to explain in plain English, but basically it demands to have a list of all the products on the system, so Virtuemart does as it is told.

The problem comes if you have
- Child products
- Multiple tax rates
- Shopping groups with discounts

Virtuemart will export all the products but for every variation, for example

product one - tax rate 1
Product one - tax rate 2
Product one - shopping group one
Product one - shopping group two
Product one - shopping group three

and so on.

So for above you may end up with the same product many times, depending on what variations it has.

So what can we do, well that is something we have been scratching our heads over since we started the design of V4. Google will only accept the rates shown on the website, other wise it will fail, if Google Checks and sees the price is different it will fail.

But if Virtuemart adds the tax depending on where you live, which is the right tax to choose, or should it choose no tax added at all?

Same as shopping groups, which one shall we choose as default.

The best way i can think about fixing this, is to add in a new format for the ID

SKU + Category ID + Child product ID
So something like this
ipod1-12-68

But thats still wouldnt work for shopper groups or different tax codes!!!

Google arnt making this easy for me i tell you!!!

If your not sure if this will effect you or not, try the demo first and check the output XML, as if the demo is causing no problems, then the real one wont either.

All the best
Ian