Purchasing a new performance part is like an investment which allows you to save money. Sure the new ones wear out just like the old ones. The difference is that the new parts have a greater lifespan and provide better service. A second hand part is usually repaired and might not be able to withstand the quality of work required by your car. For example a dealer would sell you a second hand air filter which would look clean. The problem would be that it would have dust settled in its parts which would not be visible to you. This would increase the fuel consumption of your car hence increasing the fuel cost. There are sites over the internet which would provide you with an approximate figure as to the saving provided by new ATV parts. It would be best that you purchase new parts which require replacing from a wholesale shop.
Body parts and other such things are important for a car as well. The thing is these have got nothing to do with the performance of the car. For that reason you must purchase them second hand. The best place to do that is over the internet. A dealer always keeps his or her commission. Over the internet you would be directly dealing with the person. Plus you would be open to a vast market selling ATV parts. This would ensure that you find what you are looking for, for the right price. Just be careful of phisher sites.