I learned a couple or three things when I laid a teak deck on the boat I built.
1. They are absolutely gorgeous but you're better off without them.
2. Don't sand them or use chemical cleaners on them unless they are so neglected you have no option - that's what wears them down, not walking on them.
3. Scrub them CROSS GRAIN and don't use very stiff brushes. Scrubbing with the grain, which is more instinctive, will wear down the sapwood faster and make them very "grainy" and rough, requiring the aforementioned sanding to smooth them out.
4. When checking their condition, wet them down and wait for them to get mostly dry - any seams, plugs etc. that stay wet longer than the bulk of the planks have failed
5. If you are laying one, don't use screws - bed them in epoxy or polyurethane goo and weight them down until it kicks.
6. Buy a boat with fiberglass decks.