During the Black Friday event, players who purchase items in the Goblin Market will receive 10% discount opportunity for the next item. However, the discount chance will be random between items in the same horizontal row.

Therefore, to be able to buy gemstone items at good prices. You will need to Buy items with resources advance to receive discounts on the next items.

This is a great example, I used 50.000 Wood to buy 30 minutes of accelerated research. Therefore I got a 10% discount on the legendary item. Discounted items will glow compared to regular items.

During the event, you should use gems to refresh the goblin market. Each time you refresh you will have more opportunities to buy more valuable items. Also, watch Time remaining to optimize your chances of purchasing items.