I agree, it is a legit question. I always ask and have been asked when I have sold. It never bothers me when they ask. I say go ahead and ask, if they do not want to tell you then I would just move on.
I see ads all the time where people are asking questions and the seller keeps bumping the ad...but never responds to the questions. If I don't get a response, I just forget about it.
They are probably replying by PM. If they answer the question in the thread, they will be bumping their for sale thread, and risk having the ad deleted. When I sell something, and someone asks something that would be beneficial for others to know, I will edit my initial post and add the info there. It avoids the extra bumps.
That should be a natural question. I usually ask why you getting red of it. I agree with previous poster pos guns go to gunshop and are not to be sold to an individual irregardless if you know them or not!