Engineer said this multi-level deck is fine, but should I be worried?

Those tall 6x6 posts are under alot of lateral stress on a hillside, and even with an engineer's sign-off, you need to verify the **racking** resistance yourself. That diagonal bracing is the only thing keeping the structure from swaying or folding in a high wind event. If you feel any movement while walking on the upper level, or if the lower balcony feels like it's shifting independently, you probably need to beef up the connections with thru-bolts instead of just lag screws. The green moss and algae on the lower sections is a sign of chronic moisture, wich is your biggest enemy. Take a flathead screwdriver and go around to every single post base and every joint where two pieces of wood meet. If the wood feels "punky" or the screwdriver sinks in more than a quarter-inch with light pressure, you’ve got rot. Pay special attention to the **ledger board** where the deck meets the house. If that flashing is failed or missing, the whole structure is a liability regardless of how many braces you have. Before you drop a few hundred bucks on a high-end stain, hit the whole thing with a dedicated wood cleaner—not just a power washer. High pressure can blow out the wood fibers and make it look furry. Use a soft wash approach with a brush. Once it's clean and dry, you’ll have a much better idea of the wood's condition. If the beams are checking (long cracks) but the wood is still hard, you're ussually fine to stain. But if you find soft spots in the main support girders, you're looking at a structural repair before any cosmetic work happens.

It’s a lot of height to manage, but if the bones are solid, it’s worth the effort. Just don't skip the "poke test" on those lower posts where the sun doesn't reach. That’s where the failures usually start.

That poke test sounds simple enough, but what about the metal connector pieces? I've seen some orange rust around the bolts on my own deck and I’m wondering if that’s a dealbreaker or just cosmetic. Also, I'm curious how you actually check the flashing on the ledger board without pulling the siding off. If the wood looks okay from the bottom, is it safe to assume the seal is holding up, or is there a trick to seeing behind it? Being a beginner at this, I'm terrified of missing somthing hidden until it's way too late.

Check those post-to-beam connections. If the beams are just bolted to the sides of the 6x6s rather than sitting in a notch or on a galvanized post cap, that's a red flag for a structure that tall. You don't want the entire weight of the deck resting solely on the shear strength of a few bolts. Also, look for soil erosion around the footers. On steep hills, the ground can wash away and leave those concrete piers exposed or even tilting. If the foundation is starting to 'walk' down the slope, no amount of bracing will keep it steady. Verify the base is still deep and solid before you buy any stain.

I’d take a close look at the joist hangers while you’re under there. Make sure every single hole has a proper galvanized nail in it—sometimes builders get lazy and skip a few, or use thin screws wich don't have the shear strength. If you see any hangers pulling away from the ledger, that’s a major red flag for a deck that high.

Also, check if the deck has lateral tension ties connecting the joists directly to the house floor framing. On a steep slope, having those extra anchors helps you sleep alot better when the wind starts howling against that massive surface area.