Handled social media for a big brand. Monthly retainer fee: $2,000. Had a written agreement.

When payment time came:

Me: "Invoice for this month's social media management is due."

Client: "We're only paying $500 this month."

Me: "The contract says $2,000 monthly retainer."

Client: "Yeah, but we didn't use all the services."

Me: "It's a retainer. You pay for availability, not just what you use."

Client: "We think $500 is fair for what we actually used."

Me: "That's not how retainers work. We have a signed agreement."

Client: "Contracts are flexible, right?"

They paid $500. I never worked with them again. Now I require 50% upfront for everything.