A really nice crossword! I twigged to the theme after 13 and 17, and for once that was actually helpful in filling in the grid :)
I'm having a little trouble parsing/understanding two of the clues, 4d and 12a, where I'm fairly sure of my answers, but haven't completely solved them.
For 4, I've found the depressed area, but I have no clue how to get there from the wordplay. Brendan mentioned not knowing the tax, and I'll add my name to that list of people
For 12, the first four words straightforwardly give the wordplay for a complaint/trouble, but I don't see how "for corporation" comes into it, unless it's just to say for body in a sneaky way.
Enjoy your weekends, everybody!