Defining deliverables is the most important. Don't assume that delivery of the same video in different aspect ratios and different resolutions is included in the price of a single horizontal video delivery.

I try to work with the same people each time. Sometimes I have more budget, sometimes less. I'm very upfront - I tell them how much I have, exactly what I need and I ask, "want to work with me on this?" Sometimes they're giving me a break. But regardless, I make sure they're paid quickly and in full. And when I have a little more, I pay them a little more. That's about half the time. Works out.

I work with a reliable team of freelancers, and I expand the list with new people and build solid relationships. Be straight; please just go ahead and state your budget. Be clear about what you want them to film. I pay them immediately when they deliver. I treat them with respect and support them.

As a freelancer who absolutely loathes billing more than what was on an estimate, most estimates I send out include a %5 contingency. This ensures any cost over-runs or small changes to scope/deliverables can be dealt within the agreed rate. At the beginning of a project, ask your freelancer how you can help keep the project within scope, and ensure your communications are consistent and curious, so that any issues can be discussed openly. If the freelancer feels like you're working on the project together, as a team, they're more likely to discuss challenges with scope/budget openly.

I come at this from a news magazine package perspective (short docs, etc). As a producer, you have to know what you want delivered in terms of sequences and sound in the environment you're shooting. Be clear on types of lenses needed, lighting conditions, drone, how many people in front of the camera, if lav mics are needed and/or boom. Even if you don't know the technical names of the gear, if you're able to be specific on your expectation of what's to be delivered (look and sound) then you can have the discussion with your DP and have them outline what that means in terms of gear and cost. You can make adjustments/negotiate from there. But it starts with detailed clarity from the producer/director.