Customers can be surprising. On one hand, they easily notice things that an engineer or product manager have a hard time seeing with their proximity to the product. On the other hand, they can just as readily ignore an oversight as "part of the package".
This week I had two interesting encounters with customers on opposite coasts. The first brought to my attention that the comma that should separate city and state in an address was, in fact, between the state and zip code. This was true everywhere in our system. It started from one form somewhere, a simple typo in the code, and was re-used over and over until it was the "standard" in our app. Not exactly mission-critical but hard to believe we have been staring at that every day for probably 2 years without noticing it!
On the other coast, a customer and I were working with some reports to identify why he had two different numbers for his registration count. Whenever we're talking inventory, my first move is to run the inventory report to see how many of each item has been sold and see if those numbers line up. As we were looking at the report, I noticed that we needed to sum two columns together in order to find the total registration fees sold. "Odd", I thought, as that should be summed up on its own.
I checked our API and found that we're actually generating the "inventory" totals from the "package" totals! In 90% of cases where organizers have a simple mapping between packages and inventory, these two reports would be the same or nearly the same. But in cases where an organizer takes advantage of the system to more flexibly sell their inventory with early-bird discounts or late fees, these two reports are most certainly not the same. It is fairly easily reconciled using an Excel output and some math but that is the step we were trying to prevent in the first place!
Lesson of the day: your customers are both eagle-eyed and blind as bats. They will accept what you put forth as The Right WayTM so test, test, test and test some more!
An "Endless Beta" web application is no excuse; your users will trust that you know what you're doing! Don't underestimate the value of a set of fresh eyes or someone with less domain expertise. Those folks just might be your future new customers.