Goof-off. Works for me!

A fresh coat of paint is a great way to spruce up any room. Sometimes, a new coat may not always fit within your budget, so here are some tips on how to remove those marks from your latex walls to make them look almost like new. One major rule of thumb is to always test any cleaning solution that you will be using on an area on your wall that is not in plain view. This way you can be sure your cleaning won’t cause more harm to your wall. For latex painted walls, the best course of action for new and simple marks is warm water and a non-abrasive sponge. Dip the sponge in the water and strain as much as possible while still keeping the sponge slightly damp. If you leave too much water on the sponge it can damage both the drywall and the coat of paint. Don’t get discouraged if it doesn’t disappear when you first scrub. It might take some elbow grease but keep in mind that the harder you scrub the more you are likely to remove paint off the walls. Gentle and slowly is the best way to go. Once you are done dry the area off with a clean rag. For tougher stains, you can use a baking soda. Combine warm water with baking soda to create a paste. Before you begin be sure to test the solution in an inconspicuous area to be sure that you won’t cause more damage. Once you are good to go, place some of the paste on a soft sponge and gently work the stain until you see it disappear. You don’t want to put too much pressure since it can remove the paint completely. Once the stain is removed, rinse the area with warm water and finish by drying with a clean rag. If neither of these work, you can also try cleaning solutions found in your local hardware stores. Follow directions and always test to be sure it will work on your walls. Happy cleaning!

I googled 409 degreaser and you should, too. It’s toxic! The only product I can think of that you could try, is white vinegar. I have had good luck with liquid Bartender’s Friend on white paint, but it’s hard to recommend a product should it fail and make matters worse for you. My friend swears by Carbona products for all stains and messes: https://carbona.com/products/

I'm not following your inspector's logic, but it might not be worth the fight. NEC stipulates two possibilities for a UFER: a 20ft #4 copper conductor OR a 20ft length of galvanized steel. *Then* there's a grounding electrode conductor from that UFER to the system. Those aren't the same thing, ie if you use a copper conductor as your UFER, you'll need 20ft plus x feet to bring it up out of the concrete.