The demo always works. That's exactly the problem.
A sales demo runs on clean sample data and a rehearsed path through the software - which means it can't tell you anything about how the tool survives your actual, messy business.
A demo is a magic trick, not a test
Every demo you've ever sat through ran on the same three fake customers and twelve tidy rows of sample data, clicked through in the exact order the salesperson has done a hundred times before. That's not an accident - it's the whole point. A demo is built to look finished in twenty minutes, not to survive contact with anything it wasn't rehearsed for.
Real data breaks things a demo never touches
Your actual customer list has the same company entered three times under three slightly different names, a phone number field someone used for notes instead, and forty thousand rows where the demo had twelve. That's where the slow queries show up, where the dropdown that only had five options in the demo suddenly needs five hundred, where the workflow someone built for the happy path meets the person who does it backwards. None of that ever appears in a scripted walkthrough.
A free trial barely fixes this
Even a real trial usually gets used carefully - one person, testing gently, on their best behavior, because it still feels like someone else's system. The real test is a whole team fighting over permissions on day one, someone importing eight years of legacy spreadsheets before lunch, and the office wifi doing what office wifi does. Almost nobody's trial period looks like that, so almost nobody's trial period tells them anything the demo didn't already show.
The ACS approach
Before we show a client anything, we ask for their real data - or at least a realistically messy sample of it, duplicates and inconsistent formatting included. We'd rather find the ugly edge case in week one than have a client find it three months after launch, because a demo we built to survive real data isn't really a demo anymore. It's just the product, running early.