I can confirm that this is a thing... a bigger thing than one might think. I run an IaaS cloud provider and I know off the top of my head several customers of ours who each maintain a fleet of VMs to do this for a variety of products. Eg: Limited edition shoes, show tickets, etc. Some of our customers who do this keep the VMs running and some fire them up only when needed. Some use custom software and scripts and some use purchased software designed specifically for the sites and products they want to beat others to.