Buy items at peak times, when there are a lot of items on the transfer market. This will keep prices of players low.
Pay attention to the online tournaments. When a tournament that calls for certain leagues/nations, their best players will rise quite drastically. Similar, when these tournaments end, the prices of these players will crash. Make use of this when buying and selling!
When buying players, always look at the number of contracts they have, as well as their fitness (for those who can't keep him on the bench for a game or two before using him). In case you see two players, one for 100 coins more but has 90 contracts compared to 2, it should be clear what the better buy is. Always look for this.
Buy a good, cheap substitute squad. Investing a few thousand fifa 18 coins in some good substitutes is much better than wasting money on consumables. Not only will you not ever have to buy fitness cards, but you'll be able to sell these cards once you no longer need them. Also you'll have good players to use in game in case of an injury or fatigue. Try to make sure these players will fit well into your main squad, chemistry wise. I usually substitute my full squad out for my benched squad every time my fitness drops to 80-85. When you do this, fitness and fitness cards will never be an issue for you.
The Art of Selling:
Selling items is the main form of revenue for your squad, so you want to know the way to sell well. Unfortunately in FIFA 18, the auction house can be narrowed down much more than in previous years, so it's a little more difficult to trade above what your card is worth. https://www.goldofu.com