Reporting Problems with Bikes
It used to be easier to report flat tires, missing seats or some other issue with bikes. Now it's not possible unless you contact customer service, which in itself drives me bananas sometimes. You used to be able to rate & write a comment after each ride, now you can't. They give you a few choices to report, but they don't include many issues like flat tires, brake problems etc.
The best way to report issues with a bike that is to press the wrench button on the dock after you've returned the bike. After you press the wrench button you should receive an email that asks you what is wrong with a bike that is more in-depth and has a free text field in case the issue does not match any of the bubbles. As a rule of thumb I wrench any bike that has issues that are safety hazards (think brakes, lights), make a bike completely unrideable (like a completely loose basket I ran into last week) or that would me not want to ride a bike even if it was the only bike in a dock.
When I spot an issue with a bike in a station I often quickly rent and wrench it so that I get the wrench report (as a matter of fact I did that this morning).