The 4 digit rule on the market is great because it means every relist is a significant change in price from the previous order.
However there is an issue with the implementation. When the first significant digit is a 1 the relative change in price is way bigger than when the first significant number is a 9. The difference is almost a factor 10.
For example A good is listed at 1001 isk. The next possible step is 1000 isk which is a 0.1% decrease in price. This is a fine amount and repeated relisting will quickly drive the price to its equilibrium.
However when something is priced at 9999 isk the next possible step is 9998 isk, which is only a 0.01% change.
The above means prices move way slower in certain price ranges than in others, which limits the usefulness of the feature.
Solution: Tweak the minimum step to always be around 0.1% by looking at the first digit. multiply the minimum step by this first digit. This means at 9999 isk the next possible step is 9990 isk, which is a 0.09% difference and way closer to the 0.1%.
When the 4 digit rule brings markets to their true equilibrium point the relist fee becomes obsolete.