What happens when dslr reaches shutter limit?

Like owlwings said, the shutter on the D3000 has an expected life of 100,000 actuations. Depending on how you use your camera, the shutter mechanism may last much longer than that. I have a friend who is a professional photographer. His main camera is a Canon 5D Mark II with close to 500,000 actuations on it. Any camera repair shop should be able to replace the shutter for you when it finally breaks. I've never had to deal with it so I'm not sure how much it'll cost to get it fixed. I plan to compare the cost of fixing the shutter and the cost of just buying a brand new camera body. If it costs almost as much to fix it as it would to upgrade my camera, I'll just get the new body and put off fixing the broken one. I was going to say that $420 is a bit high for a used D3000, but it looks like the price has gone up a lot since I last looked. You used to be able to get a brand new D3000 kit for $430. Now, if you're planning to include the lens with the D3000 body, I think $420 would be a reasonable price to ask. If you want to keep the lens and use it with another Nikon body, you should be asking less for it. Somewhere around $300-$350 seems to be the going rate for used D3000 bodies right now. If I were you I'd check local websites and do price comparisons to make sure you're not over or underpricing it.

The shutter on the D3000 has been tested to 100k operations and that quoted figure is almost certain to be on the low side. You are well within the quoted life of the shutter and shouldn't worry about it. Any buyer who is nervous about buying the camera is either inexperienced or is the sort who can't buy anything unless they can knock something off the price. The camera will not stop working as soon as you reach 100k actuations. All that usually happens is that the timing may become less accurate. If you are selling it, that will be the new user's problem, not yours, since the camera still has 86% of its rated shutter life left. Research eBay and other sites which sell second-hand cameras if you are unsure of a fair price to charge. You will want to set a price somewhat lower than professional sites selling refurbished cameras. Make sure that you compare prices for the same thing - body only or body + lens ... and don't forget any accessories you might want to add as an inducement!

When your DSLR reaches it shutter limit it is like your car reaching the mileage limit of the warranty. It may keep going or you may have trouble with it any day. I have a Canon Rebel and it has a shutter limit of 100,000 or less. I am now on the second 100,000 pictures and it is still going great and taking great photos. Some day I will get an error message and I will have to have it checked out and decide if the cost to repair it is worth it or not.