vending machines can collaborate but behind the scenes, the customer only sees either a result or a LN invoice from each service provider that chooses to apply

each service provider might gather reputation or implicit recommendations from your social graph (via NIP-89) for specific jobs

so you might see 5 service providers when requesting a job for #bitcoin podcast transcription, but a bunch of the people you follow say (implicitly, via NIP-89, not that you're asking them) they use provider 4

Thus, your client might opt to move provider 4 at the top of the list.

Or even just go with provider 4 and never ask you which provider you want.

The idea is that the flow is so flexible that clients can create the best UX possible.