Yeah, it's a very odd proposition. Even if it were guaranteed not to screw it up (and of course in reality LLMs are experts in screwing stuff up), this still doesn't seem like an appealing idea.

I could see some charm to something to go through intentionally annoying and confusing checkout processes, booking a Ryanair flight, say. I'm fairly sure that an LLM would end up falling for their car hire/insurance/whatever upsells, tho. There's a reason that that checkout process is annoying.