re: Is this contractor on crack?

Is he actually building it out of pine? I'm not aware of contractors using pine in that environment. The price to do it right is much different than the DIY price.

10' will require engineering and permits

Should be built out of weather resistant wood (not any variety of pine) or an engineered product.

Let me make sure i understand, you two guys were going to build a 10ft high 500sqft deck partially over a canal in galveston?

Whats the wind/uplift load on a deck that size? What are the approved structural connectors for deck to pile and piles to footings? Just curious