When looking for HVAC replacement parts online, it is important to consider the reputation of the seller, the quality of the parts, the price, and the return policy. The seller's reputation is important because you want to ensure that you are buying from a reputable source that will stand behind the parts they sell. Many fly-by-night websites sell low-quality parts and then disappear when you have a problem with them. So, checking out the seller before making a purchase is important. The quality of the parts is also important. You don't want to end up with parts that are not going to last or that are going to break easily. so it is important to find a seller that sells high-quality parts.