One question that changes how you approach every inbound brand enquiry:
"Is this brand already buying UGC from someone else?"
If yes: they have budget allocated, they understand the process, and they're looking for a replacement or addition. Your job is to show them you're better than what they have.
If no: you're potentially educating them on pricing, process, and value from scratch. That's a longer sales cycle and requires a different approach.
How do you find out? Ask directly. "Have you worked with UGC creators before?" is a completely normal question that tells you everything.