Let me revise things were previously said in the above comments here, these all are available for you as a seller ;
1- Create a gig with a service in the field of your profession.
2- Describe your gig elegantly and clearly, to more empress the customer, and to avoid customer’s uncertainty as much as possible. Additionally, write what you need (like info and data) from the customer, in the requirements of your gig, so you find his/her request described just in time the order is placed, that’s how you save some precious communication time.
Note: the customer needs to feel he/she has been understood by you, in order to be trusted and repeated seller. That will reduce the time spent in the next step.
3- keep in touch with the customer especially from the time the order is placed until the point you are able to start work, that makes you feel comfortable while proceeding with the needed work. Stay online during the working phase to be ready just in case the customer comes up with new inputs, so using the Fiverr app on your smartphone is recommended to be notified by the site when you are away of your office". Then if the new inputs provided by the customer require an extra time exceeding your determined delivery time, make an order dispute and ask the customer politely for a delivery time extend or expansion, then the order will be given some time to wait for the client response.