There's no way you're in this conversation without being aware that scalping is a controversial practice at best.
https://theconversation.com/the-economics-of-ticket-scalping...
That doesn't make them right.
It doesn't matter if it's legal, it matters if the website owner doesn't want x doing y on their site. A bot consistently not abiding by owners' intent is inheritly malicious.
The LinkedIn case shows that it's not illegal in some cases - would you classify the behavior of the defendant in that case as malicious?
When I've run scraping software in the past I used DigitalOcean, which doesn't contain a requirement to abide by robots.txt. As far as I can tell it's both legal and consistent with their ToS to run a program that makes purchases on a website.
In my experience a lot of bots seem to be running on hacked servers or through hacked/insecure proxies. I'd imagine tracking down the owner or someone upstream of those boxes could be effective in taking them offline.