Which TikTok Shop operational bottleneck slows growth the most?

For teams running multiple TikTok Shop stores or markets, the bottleneck tends to move as volume grows:

- reconciling fees, refunds and ad spend

- finding products that hold margin after discounts

- sourcing creators who can produce repeatable sales

- testing enough creative without wasting budget

Which one is usually the hardest to solve in practice, and what process or tool has made the biggest difference for you? I am especially interested in answers from sellers operating across more than one market.