Would just like to add to this as a newcomer using this guide --
If there's a high server population, and not a lot of APD on, would not recommend wreck excavating at Kavala. Go to Pyrgos, go 2.8km southwest by boat, and excavate there. Sneak through the back alleys to the Jewelry shop when done -- there's even an ATM right on the back side of the building.
Reason I'm saying this is because the beach at Kavala to land at is heavily open and watched by petty robbers and lone wolf thieves, just waiting for you to return and follow you to rob after selling to jeweler (speaking from experience). Yes, you're adding about 5 mins to your Wreck Runs by going to Pyrgos, but it's a hell of a lot less risky.