I just want to complement you on you handling of the review. To many a-time developers get in to a rather pointless discussion that only leeds destructive back and forth allegations. This, I think, is the way to do it. After all, it is a customer and the customer "is all ways right" and entitled to his/her opinion, which is not to be taken personally. Provided with relevant info and the additional info he/she should be content, do their evaluation and make their decision whether to accept what's offered or not. And this my friend you accomplished to a tee.
(Note: I am not commenting on the review it self, just the handling of the customer by the developer)
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