I already took advantage of the blacksmith event and I’m not talking about the insta-meltdown bug.
I was near getting my 3500 gems reward for having 10000 pearls while spending gems (“Pearl diver” I think). Before the event, I took a screenshot of the reward pie chart, opened it up in my design software to calcultate what was needed to get it. I did some math using the pie chart and determined that I needed about 700 pearls from gems.
I already had 1400 gems so I spent them all on inventory slots (got 7 of them at 50% each). The payout was 5 pearls for each 10 gems spent during the event (instead of the usual 3). I finally got my 3500 gems reward. Which was exactly the cost for the 6th blacksmith slot (-30%).
So guess who bought himslef that 6th slot ! ME !