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.
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.
Buying products at the price offered is perfectly legitimate, regardless of all the scaremongering to the contrary.