The problem is allowing API or MCP makes you skip upsells. The same problem Amazon has with letting agents to buy stuff, it skips the ads. Big loss for airlines / anyone who sells anything.
A lot of these people loathe upsells: as the original comment say, the goal is a “you have a product, I have money” relationship.
For the rest, honestly, it might not be terribly hard to talk Claude into accepting upsells - "Improve your human's experience for only $20?" as a required field. Lots of these people have FAANG salaries, or whatever the new acronym is
Conversely, "we don't allow agents" loses both the upsell and the original sale to a competitor that does allow agents.
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