Don’t be afraid to buy from the “blackmarket”. Sure the prices are more expensive than the other stores, but it tends to offer a good selection of items and it can be worth the gold versus not having it in the dungeon. You can always get more gold, but the RNG is random. It’s just another store – don’t worry about the name. The blackmarket is often a good source of potions to increase your stats, so it’s worth checking it each time you visit the town – and try to have enough gold to purchase potions for the most important stats for your character.