A few years ago, a customer ordered some match strikers from me that needed to be delivered overnight to her client who was getting married over the weekend.
She contacted me before she made her purchase, asking me to confirm if I was able to ship overnight, and as far as I knew, I could.
I live in the north Metro Atlanta area. If you're familiar with Atlanta at all, you know that traffic is...a mess. I was working my day job at the time, and I knew that in order to guarantee overnight delivery, that my package had to be dropped off at the post office before closing, preferably scanned by a postal worker at the counter.
So, I decided to go out of my way, way across town, to go to the Airport hub -- the major post office processing center about 10 minutes from the Atlanta airport. I knew the cut off time would be 7PM. When I got there around 6:30 PM, the line to the counter was very long, so I decided to drop the package in the lobby postal bins. Hey, it was before the cutoff, so I figured I had made it.
I really should have waited in line to have a postal worker scan it. Just because you put a package in the lobby postal bin, even well before the cut off time, doesn't mean that your package will actually be accepted and processed that day. Little did I know that my package would not be accepted until the next day, and it's the acceptance date and time that actually starts the clock on your shipment.
In the end, the package did not get shipped overnight. My customer was very upset. I doubt that this ruined her client's wedding, but I'm sure it disappointed them and maybe made them question her. I reached out the customer repeatedly to apologize and try to make things right, but she never responded, and I totally understood.
This happened almost 4 years ago, but as you can see, it has stuck with me ever since. This incident taught me an important lesson about how our postal service operates. Since then I have built in buffer times for overnight or even 2nd day shipping. If I know I can't get an overnight package to the post office (or UPS or FedEx for that matter) well before the cutoff time, or allow extra time to wait in line to have a postal worker scan it (and even then, sometimes there are still delays), then I tell the customer upfront that I cannot deliver overnight in that case.
I don't like telling people "no", but sometimes I have to do that in order to set realistic expectations. It's better to tell a customer "no" or "not now" and disappoint them upfront, than to to not be able to deliver a product on time, and then deal with anger, frustration, possibly bad word of mouth, and no repeat business.
Having realistic expectations about what you can or cannot do within a reasonable amount of time protects both you and your customers. They now have an option to go with another seller, and while you'd certainly prefer to have that sale, having peace of mind is even better.