I think you might be looking at the issue wrong. First, you know the rules. Fiverr can't guarantee sales, clicks, etc. Secondly, if your position is exactly the same. It might just be the market trends. Check keywords traffic on Google, for example, some keywords are known to bring in 10,000 visitors per month or more for the first position website. But that doesn't mean that they always will. That's just an estimation based on past performance. Any time a keyword or market trend can drop or rise in search volume.