[What are some common challenges faced by website developers on Fiverr and how can they be overcome?]

When a customer is not clear about what s/he wants and you can't understand them clearly it's maybe better to not accept the customer. I've had situations in the past where a customer was using Google Translate which can make our job really hard.

[Grammarly feature CSS is not optimized]

I agree with this one. For now what I do is typing enters (shift enter) in the field so I can read the last part of my message.