That is a bad business practice. That would be enough for me to never do business with them again and to post bad stuff about them all over the place.i tried to order from them a couple times. i loved the prices they quoted for glass for a plywood tank i was building. even paid for the glass becasue they said it would be delivered on a certin date. turns out they decided to cancel the delivery due to someone elses order that was placed after mine. becasue of this they told me it would be another 3 weeks before they could get my order to me. i did get a refund for the glass but i think it is bad buisness to quote someone a delivery date and then the day before tell them that they could not make the delivery becasue of someone elses order. i chose to support a local buisness even though it cost me a little bit more.
If you have a paid for and confirmed order with an agreed upon delivery date, they should not push your order back because they just received a more expensive order from someone else. What if you were depending on having your material at that date to meet a build schedule of some sort that was not flexible? They would have just given you the shaft.