Believe it or not, there are different kinds of auto parts. If you need a need tire, air intake, engine or side mirrors, your options are varied. Knowing these differences can mean your car breaking down in a week or in ten years - so it's important to account for them and make a proper purchasing decision.
New Parts - Generally, these are your best bet. They're fresh, but with freshness comes price. Many people can't afford a brand new engine, but if you want the best performance, consistency and sense of reliability that comes with new parts, they're the way to go. However, you can sometimes find other types of parts that are just as efficient, however, the risk is higher and the rate of success is lower.
Rebuilt Parts - Major auto parts are normally made up of a few smaller parts. When one part ceases to work, it may have to do with one of the smaller parts malfunctioning despite the majority of them still working efficiently. Using rebuilt parts means they will seek out this one misguided part and replace it while keeping your others in place. Doing this will save money, however, often times the mixture of old and new components will mean you may have to replace the larger part in its entirety due to the other parts being worn.
Used parts - Buying used parts from a salvage yard is a cheap option. To evaluate these, look at the conditioning of the yard and the parts. If both seem low quality, move on to another salvage yard. This option can provide a high return but it also comes with the high risk of buying such a cheap option.
Remanufactured parts - This basically describes 'recycling' old parts into new condition. This generally involves disassembling, cleaning, inspecting, replacing parts, and then re-engineering and testing the product before it is returned to the working world. It has to meet OEM standards to be reintroduced to the marketplace. The good thing about remanufactured parts is that they often carry a strong warranty that will offset any worry you have about purchasing 'remade' parts.