1. Decide which is more important the specific item or the desired deadline. There are often alternates that can fill the same function if you have flexibility.
2. Just because it is "in stock" does not mean that it is "on hand". Plenty of places won't clarify that their out of area warehouse is going to have to send it to them first.
3. Arrival dates are meaningless without tracking numbers. Even a tracking number that has been generated isn't helpful if the item hasn't been picked up or scheduled for delivery.
4. Always inspect the contents to make sure everything arrived. Too many times companies will ship incomplete orders just to tell you that "it is on the way".
5. Don't be fooled by websites claiming they can deliver what a professional has told you is not available. Many will try to convince you once you call to complain that nobody can get it faster so you might as well just stay in line with them.