I’m sure this has been suggested before, but I haven’t seen anything recent so I’m going to toss it out there. People so often complain on the forums about problems using free gig offers and free gig credits. Coupon codes would be an excellent solution to that alone.
The second thing that would be great for buyers, sellers and Fiverr is that if coupon codes were somehow available in other ways it could bring in more buyers and more revenue. Perhaps sellers could give away a certain number of codes per year after level 1 (to avoid people using them to get manipulated reviews before some proof of ability.)
If necessary, Fiverr could charge extra commission to the seller for gigs bought with coupons which would also help avoid abuse of the system. Another option would be to sell coupon codes to sellers but again keep it at a particular level and limit the number available in a set time period.
So, if available only by Fiverr as a start, buyers would be a lot happier with their freebies over the current messy credit system. That could be a test case to see how it worked. If also available to sellers down the road, I think everyone could benefit.