Most Costly Location Mistake for a Beginner Scout?

Hey everyone,

I'm still pretty green as a location scout, currently trying to lock down spots for a low-budget indie feature. I've been doing my best to avoid rookie errors, not just relying on Google Images for a place, always double-checking access, and being upfront about the crew size, even if it's small. I recently found a fantastic old diner that would be perfect, but the owner is a bit wary of anything 'Hollywood,' even though we're anything but.

It got me thinking about all the ways things can go wrong. In your experience, what's that single, biggest, most expensive blunder a new scout is most likely to trip over? I'm trying to foresee and prevent, so any hard-learned lessons would be invaluable.