I don't think you understand game design if you can't understand what's meant by "ruining the economy." It means that the player gets so much money that there's essentially no use for it anymore. They can buy anything that's available without concern. For example, in Morrowind you can craft potions with ridiculous value, then use that to pay for levels from trainers and buy the best items, then pay for enchanting to make them even better. It trivializes the game.
The only option at that point is to just limit what can be purchased. That's a much worse solution than balancing the game's economy so the player has options to spend money on, but critically they can't buy everything. Video games are about making decisions. If you don't have to decide anything than why not just watch a movie? The game needs to present you with options, and you need to choose what you will and won't do. The economy is a great place this can happen in a game that's balanced well.