You are right, Mafia Salad, always try to think of alternatives to avoid the interaction, if possible. However, there are instances where you can't reasonably do so, and in these cases, giving the PD a heads up (via email) is a very good idea.
In your situation, Mykey, if someone is sending you, and your dictator has no subordinates, you have little choice. Make sure the trade is a fair one. I guess this would go for if someone is sending you or not, for if you need oil, and there is no other viable alternative location, then you have little choice in the matter.
If you are trading in general in a town where you have another character, and your other character has what you're looking for, or needs what you have..........number 1, you cannot send your trading char there on purpose just to benefit your other char. Number 2.......you must call out the requested trading outloud, and give other characters the chance to trade with you first. If, after a couple of chances and a couple of days, no one takes you up on it, then it is okay to trade with your own character, as long as the trade is a fair one for both sides.
One comment related to your question, Pie. Not only is it a CR breach to have more than one character in the same government/company/religion etc., but it is also a breach to have more than one character actively supporting the same issues, political or social of the same area. This can be a tricky one, if you have chars in different towns, and the issue becomes far reaching, and both chars would naturally be on the same side of the issue. Just be careful and try to have one of them not "actively" pursuing or supporting it. (Am I making any sense? I am in my own mind

)
However, in your situation, Pie, if it is something like the above, and your first char is already active in the issue DO NOT SEND YOUR OTHER CHAR! That would be a serious CR breach. If your char that already lives there is not involved whatsoever in the reason your second char wishes to go, then it may well be okay. It's so hard to say, without knowing the details.
If you would prefer a better answer, you can write the PD with those details, so we can better inform you.