The only crossword I (attempt to) do with any regularity is the Observer one, with a success rate varying between, say 75% and 100% of the clues. From what I've seen of this crossword, I'd say the 'rules' are quite stringent, and doubling up letters is a definite no-no, as is anagrams of words that have to be inferred and don't actually form part of the clue.
Still, this is an amateur thing, and why should we follow whatever rules there might be exactly? As I said above, I found a recent clue very convoluted and didn't 'get it' but somebody solved it quite quickly.