I don't know that pirl was so irritated that she was asked, per say, but that the person asking was rude in the way they asked and completed their demand with instructions. That would irritate me also, even if I DID have the plants listed for trade. I would decline just for spite
I think a real issue here is using curtsey and manners. Be polite, be to the point and accept no for an answer.
I do think (not in pirl's case) that some members however indicate they are interested in trading but then do not do a very good job of keeping their trade list up to date. There have been times I have been interested in a plant someone had listed a year or two ago. Even though it may not be listed for trade, it is obvious they have other things for trade and the list is outdated. I don't see the harm in sending a short polite inquiry asking if they have it available for trade. I think it is important for members to update their list a couple times a year or more often if needed so that other members can tell clearly what is is or isn't available. This would of course do nothing for the folks coming in off the internet through a search or people who just join and ask for plants. But it would make trading a little nicer for those of us who are regular members.