Clash Royale Gem Refund Questions

Did some reading around and learned that they put your gem balance into negative after refunding.

- Would I be able to earn gems legitly through chests to fix the gem balance?

- Between Apple and Google in-app purchases, which one is known to be more successful?

My plan was do do $200 (100x2) purchases on a credit card and spend the gems and attempt to refund. I've seen threads with limits as high as $500, but unsure if in-app refunding is still easy to do.

Thank you.