Would the ladies ever offer a discount to someone who wrote a
negative review about them? If so, then I don't see a problem with it.
Otherwise, like TomCat alluded to, it amounts to nothing more than
Quid Pro Quo. As hobbyists, we depend on factual, honest reviews to determine how best to spend our time and money. I, and I'm sure others would agree, don't want the Reviews section turning into a collection of "paid advertisements" like those you see in magazines disguised as an article hawking some new product.
ETA: A better idea, ladies, would be to offer discounts to repeat clients in order to keep them coming back.