With a bit more digging I've found a couple of references to coupons and discounts which may explain my problems.
The first mentions as tj1 has to setup coupons in GC seller account under settings, well there are no options in there that I can find to do this in either our sandbox or real sellers account.
Next I reread the developer notes and noticed
http://code.google.com/apis/checkout..._and_discounts
The key part being
It seems that coupons are handled by the Merchant Calculations API which at the moment UK Merchants don't get.
- Use the Merchant Calculations API to compute discounts after the buyer reviews the order. If you choose this option, the customer will have the option to enter coupon or gift certificate codes on the Google Checkout Place Order page. This option requires you to create and operate a fast, highly reliable web service to compute discounts. (That service could also calculate tax and shipping costs.) Please see the Merchant Calculations API section for more information.
- Note: Merchants in the U.K. cannot yet use the Merchant Calculations API to calculate coupons or gift certificates.
So that along with Zen not posting group discounts probably explains why it won't work for us at the moment. We can't really release the GC integration on our site until this is working as trade customers can't buy via it as they get different prices to joe public.
If anyone knows if the mod is likely to change anytime soon to integrate discounts being posted to GC then it would be great to hear. In the meantime I may have a look at the code myself but I fear it's going to be a little bit above my talent.
Cheers
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