Based on my experience as a seller and buyer I can say the 3 biggest mistakes sellers on Fiverr make are:
Late delivery. Your buyer will most probably leave you a negative review and never use you again so rather manage your time and set a reasonable delivery date instead of failing to deliver on time.
Poor quality gig delivery. Always over deliver. Let your buyer feel that you’ve gone the extra mile and really put in the effort to complete the gig order. This makes the buyer super satisfied but also feels special.
Avoidable mistakes. Always use clear communication. Be super clear about your gig offering. If you don’t understand your buyer’s requests rather ask the buyer to clarify. Rather ask questions than get it wrong and receive a negative review.
I hope these tips help you to be better sellers and receive more repeat orders!