Try not to let it bother you. I also sell stuff on craigslist sometimes. With sales, there are some people who always ask twice what they really have to have because there are some people who only feel happy about the deal if they have dickered the price down. There's no harm in asking, and I have found that the majority of the people who respond to my ads don't know anything at all about the value of what I'm selling. So when they ask I just politely say the price is firm, or you could even put that in your ad. However, most of the people who contact you will still not have paid any attention to what you wrote in the ad, so be prepared to answer all the questions you already put in the ad.
Like, is it male or female when you advertised a hen, or how old is it when you said it's a year old, etc etc etc.
But in the end, about half the time when I've answered all the "dumb" questions for the person, I've educated them enough that I make the sale after all and start somebody off right with chickens or turkeys, so. . . it's worth it to be patient and not take it personally. Best Wishes!