If you need to do a basic credit to a customer and return inventory then you can do that as a negative sales order line in AX. There is a button on the sales line called credit note that helps you find the original order to credit. This is a quick walk through of that process.
An alternative way to do this is via a return order which you can see an overview on this post.
Cheers
Lachlan
OrganicAX 
Is there a parameter that will also display the credit note (i.e. the negative transactions) in the credi note selection window? AX 2009 allows them to be visible but not AX 2012.
Regards,
Eric
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HI Eric
I don’t believe there is a parameter in AX2012 for that. What is the reason for needing it? Is it so you can try to see if something as already been credited?
Cheers
Lachlan
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