Does the factory store in Delft have lower prices than the shops in Amsterdam that deal in the real thing (new --not antique-- but real Delftware)? And is there a Delftware shop in Haarlem?
I don't know about a shop in Haalem. We visited the Delftware factory in, of course, Delft. The prices were shockingly high. I would say there are no bargains there although the self guided tour is very interesting.
"Delftware" is like an "appellation d'origine contrôlée", it's not a specific brand made by one company. In addition to De Koninlijke Porceleyne Fles factory, there's also a number of smaller artisinal ceramic shops throughout Delft, but I doubt you would save any amount of money. I think the experience is more of the draw, not the price.
The factory store in Delft sells "seconds," which have some minor flaw in them, for about 1/2 price. I couldn't find the flaw myself in the piece I bought. They also generated the VAT refund forms for me, so that it was very easy to get the refund at Schiphol Airport at the end of my trip. If you love porcelain, the factory tour was worth the admission price, but you don't have to pay to visit the gift shop (of course!).