I haven't had any issues with coin, and I didn't use any money exploits. I have, like every other RPG I ever play, done alot of collecting and selling of stuff. And I'll hold on to some stuff to see if I run into better prices at other merchants. There's a merchant in Toussaint near the cemetery, inside the two story tavern. It's the place where you get a Witcher contract about loud noises coming from the cemetery, and the merchant is someone you need to save from a sidequests (about three brothers). I mention it because he will buy everything at full price. His pouch is small, but I wind up buying all his food and wine and offloading weight and selling jewelry at full price at enough of a pace that I see a rise.
I'm pretty sure they adjusted prices, too, for weapons and armor you pick up from bandits to sell off. I'm looking at maces, warhammers, and swords I'll never use going for 150-350 crowns. Raid enough bandit camps, find enough guarded treasures...all of those have helped me alot.
I just finished Blood and Wine...and holy hell was that amazing. It's amazing how much content there is for the price (I paid $17.99, it was at a discount right before it launched on PSN). There's a ton of stuff, there. Alot of replayability and the storytelling is as amazing as you'd expect from CDPR. True to The Witcher name, it's pretty subversive too. The story, and the themes, they touch on go places that are very interesting. The manticore gear was awesome, getting to see Geralt in his Witcher 1 attire. The ending was perfect, too.
Nothing but good things to say about Blood and Wine, really.