Thanks Alan,
So what we're currently trying to understand is since these one off retail sites are only using Paypal and or Google Checkout it should just be a matter of directing one outgoing link from all sites 'Buy Now' so it will redirect to our store on shop.abc.us and SEs will consider this like any other outgoing link?
Our reasoning is by changing only one element "Buy Now" buttons the SE is looking at these out going links to Paypal and Google Checkout already so 301 redirecting to our site now shouldn't affect SEO.