How long to leave an animal up for sale?

This is a question that has always bugged me. There are animals up for sale that are there for months. When that happens something is obviously not right. It seems that the general public is finally desensitized to our ad because of the permanent exposure. Should we decide to pull out the ad for a while? Should we change the price? On an animal that has been up for sale for weeks with no inquiries, when there are hundreds of people viewing it weekly, it seems obvious that we are either overpriced or there's a lot of competition. So in this example, what would be your strategy as a seller:

The huge influx of people entering the breeding/selling arenas has had a variety of effects.
For starters, there are more animals available from a much greater number of people. New or not, sellers have different perspectives and priorities - some are more focused on the sale and will drop prices til they get it, others would rather hold onto the animals and (at least on the face of things) try to get their price. In its simplest form, this creates a good market for buyers, as, if they become interested in an animal that is a bit outside their price range, all they have to do is wait. Somebody will come along and offer it for less money. A seller may start dropping his price, or decide that he needs to start moving animals & take lower offers than he initially would have.
Another factor that has been coming into play more and more (and even MORE lately) is the economy. Its affecting buyers and sellers. Heating, feeding, and supply expenses are all increasing. Shipping prices are becoming almost prohibitive, in some cases. People look at what they are paying for groceries and gasoline, and think about this winter's heating costs. More and more people are thinking twice, and stepping away from that extravagant snake purchase (I'm guilty of this myself - I had been on the verge of purchasing a new male to spice up my boa projects...but between expenses & my thoughts on the likelihood of being able to sell the offspring, I've pretty much decided against it. though anybody that knows me knows I am going back and forth on a regular basis, and it won't take much to push me over the edge, lol

As for the initial question, it depends on the animal & the seller. Personally, I think I price my animals fairly...and if something does not sell I won't take low offers (there are rare exceptions, when I just want to get rid of something). I'd rather wholesale animals to vendors at a show than take 50-60% of my asking price from an online customer. More often than not, I just pull the ads...but some animals just need to be available when somebody is looking for them. I've left ads up for months, then gotten an excited response by somebody that just came across it. (I'll assume that, by leaving ads up, you mean keeping them active, vs letting them drop 6 pages back...sometimes I do forget an ad, but I try to keep them current).

I have removed my ads if they do not sell after a while (of course I have only posted 2 ads to my knowledge)

I would say you don't necessarily have to pull the ad altogether. But, I would highly recommend changing it up. If there aren't pictures, post some (the more the better; and more likely your success will be). If there are currently pictures, either remove them and add newer pictures, or completely change your ad so that the wording and format is different. This will get people more interested as it is no longer the "same old ad". If people see the same ad over and over, they will avoid it and not even look down past your first sentence. If you're not getting results, change it up. I would suggest doing an overhaul every two to three weeks for an aggressive approach to a sale. Price reductions also work, but be sure to make known what the original price was and make the reduction significant enough to get people's attention. If your original price was too high to begin with, people may not think much of your reduction as well. Try to make your reduction roughly 10% less than most of your competition is asking. This has usually gotten me a sale (with money in my hands) within two days of posting a reduction price on other sites.