Do you think it's bad if I'm critical of a delivery service I've used?
Did you have an issue with their service?
My order is always late and often wrong.
That sounds frustrating. Since it's happened several times, it sounds like they're not very reliable. Giving them a negative review would help others avoid them
I'll post a negative review online so others know what their service is like.
That's a good idea, other people show know how the service is. It's unfortunate, but after repeated bad experiences a negative review is warranted.