When looking for vehicle seats for sale, you need to know the make and model of your car so that you can be sure you get vehicle seats that fit it. Adapter kits are also available for custom seats.
Make sure you know whether your car has power seats or mechanical ones. Mechanical seats can generally only be replaced with other mechanical seats. Power seats can be replaced with other power seats, which are more expensive, or you can downgrade them to mechanical seats.
Understand the benefits of buying used or new. New seats are nicer and have better resale value if you sell the vehicle, but they are also more expensive. Used seats are significantly less expensive but may be stained, torn or otherwise damaged. It may also be harder to find a used seat that matches your vehicle's upholstery. Salvage yards may be a good source for used seats, although you may need to use an adapter kit if you cannot find an exact match.
If you plan to install the seat yourself, make sure you understand the tools and procedures to do it. If you have never done it before, ask the seller to include instructions. Having the seats professionally installed may be worth the additional cost if you are not experienced with vehicle interior repairs, especially on newer cars with power seats.