You are sometimes better off buying from US sellers.
When buying button batteries, you can get some from US-based sellers for just a few cents more, and get it within a few days instead of a few weeks.
Some items like memory cards have a very high rate of non-working or less usable space than claimed when bought from china.
Chips or other accessories for which compatibility is tricky and critical.
Anything that you want sooner than 5 weeks!