Freelancers/Contract Workers: Is it normal to be paid by a hiring agency ONLY after their client pays them for the production?

So I'm in talks with a local advertising agency about doing their clients drone photography/video as a contract worker. The thing is, their proposed way of paying me seems off.

Rather than doing NET30 for the work, after the client approves the creative, they instead want to pay me after the creative is approved AND after the client pays them. So I could be looking at 60-90 days to receive payment, and potentially not getting paid at all if their clients don't pony up.

So, to anyone who has ever freelanced with an agency: is this normal?

This agency says that they have been doing this with all of their vendors/subcontractors for years, but it doesn't seem very industry standard to me. It would be like doing photography for a real estate agent and only getting paid if they sell that house.