I think we need a dependable US Postal Service. I'm glad to hear that someone has success with the USPS for their business. I have never bought chicks through the mail. I always get mine at the local Co-Op the day the hatchery truck delivers the day old chicks.
I have a few bones to pick with the USPS. I live out in the country, and it is not uncommon for me to see other people's mail in my mailbox from time to time. I just put the mail back into the mailbox and lift the flag for the carrier to pick it up the next day. I hope that my neighbors would do the same.
However, I have ordered packages from Amazon and a few get sent via USPS. The tracking service by the USPS is not very good where I live. I have had some packages reported as delivered, but I never see them. I have had some packages delivered but the USPS tracking lost track of them in their system. I cannot remember a time with tracking problems with UPS or FedEx, in comparison. IMHO, USPS needs to improve their tracking system to get to the level of UPS and FedEx.