This is a real story, but the actual names have been replaced in XXX, just not to make other people look bad
There is this site called xxxxxxxxx.com that charges you $XX membership access. Having just moved from Canada, last year I didn't have a US credit card to pay the fee and tried to use my Canadian visa. Problem: the input field for postal code (zip code) accepts 5 characters only, since the zip codes in US a like 90404, 90066 and so on. A Canadian postal code is like H0H-0H0 or H0H0H0, six characters. So seemed like I couldn't pay online. Or could I?
Checking the source code with Firebug gives me this:
From here it's trivial to change
maxlength attribute of the input. Even with IE it's super easy just to type in the address bar something like:
So I did change it, typed my Canadian CC#, Canadian postal code and submitted the form, crossing fingers that the developers who built the site were too pressed by deadlines to do a proper server-side validation. Lo and behold, it worked!
At the end with the help of an innocent client-side tweak I got what I needed (membership), xxxxxxxx.com got more business, and everybody's happy.
There's a lesson in this: sometimes being too strict in data validation for things that don't matter is just in your way.
And another: don't assume all your potential clients are from US.