Top Gear Australia: Not again!
If there's one piece of advice I could give to every company that has customers, it would be "under-promise, and over-deliver".
It's expectation management 101.
I have a vendor whom we regularly have to deal with. This particular vendor will regularly promise that a release will be delivered to us, with certain features, and "by X date". Every release, that date slips by around 14 days, and is missing a number of promised features.
It's okay to make a promise a customer, but if you make that promise, be damn sure that you're going to meet it. When promising a date, always allow yourself a margin! A customer is always happy to have a product delivered early, and very rarely happy for you to deliver your product late.
When your product does not meet the expectations you have set, it undermines your customer's faith in both you as a vendor, and in your product. On the other hand, when your produce exceeds expectations, you generate goodwill.
I recently organised for shipping for a server. The company advertised "overnight delivery!" - but the delivery actually took two days to arrive. If the company had advertised "48-hour delivery" now, that would have been fine. Even better if they'd advertised "48-hour delivery", but actually delivered overnight!
Managing expectations is easy. Under-promise, and over-deliver.