Is when the customer is right and there's nothing you can do to help them.
I work for an online customer-facing online solution. We have a few different price points with free trials available for all of them. You can't move to our lowest price point if you didn't sign up for that price point's trial. If you started another type of trial but end up wanting the lowest price point, you have to start a new trial. This is made all the more enjoyable by the fact that usernames and emails can't be used twice on our system, so you have to contact us to cancel/deactivate your old account to free up those credentials for the new account.
There are technical reasons for this – the lowest price point offers very few features and we have to manually disable the features not included with that price point. We also want it to be something of a hassle to get that lowest price point. None the less, this isn't a scalable option.
Someone just called me wanting to move from a mid-price trial to the lowest price point so they could pay us money for services. I had to instruct her on how we do this. We deactivated her old account, but when I started walking her through setting up the new account, she was like, 'what?! I have to do all of this work again?' From there, she became (rightfully) more frustrated. She said she couldn't deal with the process anymore and hung up.
This has been a bit of a thorn in my side for a while. I spoke with my boss about it but he just reiterated that we shouldn't make it easy for customers to choose the lowest price, especially since we'd have to do the legwork on moving their account.
So we lose potential users and their money. You know who deals almost exclusively with these users? This girl. My job isn't very high pressure but conversion rate is a metric they use to measure my performance. When shit like this happens, I'm the one who has to tell the frustrated customer that our system is stupid and I'm the one who looks like I fucked up if they don't end up paying. It's a really tough place to be in – telling the person on the other end that you understand their frustrations without putting down your company.
Anyway, now I'm frustrated. As the user said, it should be easy for her – if anything is difficult about this, it should be our issue to deal with, not the customer's. I hope she calls back.