When a potential customer fills out a form and submits it, they might make a mistake. Hey, it happens, but that’s why your web developers wrote code that will send the form back to the potential customer with a message kindly telling the user what field was missing or filled out incorrectly. When we say kindly, what we mean is that an average human, not a web geek, can understand the language. Good: “The username you selected is too long, please choose a shorter one.” Bad: “ERROR: user_id too long!!!” Which message would you rather see?
I’m also sure your developers took the time to make sure they pre-populated the fields the potential customer filled in correctly so they are not forced to fill them in again. Not just the text fields, but the radio buttons, checkboxes, drop-down lists, textareas, etc. You’d be surprised how many developers don’t do this. Yes it’s extra work, but who would you rather to do the extra work, your developers, or your potential customers? (Hint: The developers should only have to do it once.)
Make things easier for your potential customers. Hopefully this will change them into satisfied customers.