So far as codewords go, it might be worth pointing out that the human short term memory has an extremely limited capacity and can only store about seven pieces of immediate information at a time. If someone has less than seven (simple) rules, the average person should be able to remember those while trading with them and the rules are thus more likely to be followed. If the rules include a codeword though, you're making the person devote more memory to keeping that codeword in their mind than they do to remembering your other rules. If it's a multi-part codeword, there's very little chance of a person remembering both the codeword and the rules. For example, something like this:
Rule 3: The codeword is apple.
Rule 5: Ignore Rule 3 - the codeword is banana.
Rule 7: If you really read my rules, the real codeword is swordfish.
takes up pretty much all of the memory 'slots' because people can't just dump the previous codeword from the short term memory and each 'command' takes another slot, so in your memory it goes something like:
1. Type codeword
2. Codeword is apple
3. Ignore apple
4. Type banana
5. Ignore banana
6. Still ignore apple
7. Type swordfish
Your trading partner has now had every one of your real trade rules pushed out of their immediate memory and will only remember that they're supposed to type swordfish. The people who actually remember your rules will likely forget what codeword they're supposed to type or that there is one at all. I've done some experimentation with this and found that the people who put the codeword in were most likely to have missed some or all of the actual rules while those who missed the codeword were far more likely to actually be following the rules. ^^
The same kind of goes for stories in trade rules - you want people to remember that you don't want trades of VCs, not that they've seen a huge winged black wolf named Raven stepping out of a dark wood. :b Stories just make it harder for people to find and remember the relevant information. I always skip them and just pick out the rules around the story bits.
For me though, the biggest peeve is rude/mean/aggressive trade rules, like "I DON'T TRADE WITH COPPAS!!1!1 IF YOU'RE COPPA I CANCEL AND FOE!!
" That sort of thing makes me nope right out of there. Especially if it's in neon colours, which it often is.
For my own trade rules, I'm always tweaking them here and there to make them clearer, but I still only get maybe one trade in 20 that actually follows them. Eh, c'est la vie. It's probably because I have more than 7 pieces of information in there.