Buy one 1U server from $supplier, specifically ask for a pair of rails, learn that « Of course it comes with rails! ».
Two weeks later. Buy a 42U rack, and eight 1U servers, all of these from the same $supplier, and at the same time. Receive your rack and 8 servers, without rails. Inquire by email: « No, servers don’t come automatically with rails, you didn’t ask for them ».
Thanks, Dell. It’s always a pleasure.