I discovered this years ago. We all assume that the dealer is more expensive, but that is not always the case. I've been buying genuine GM (Delco) windshield wipers, because they last much longer, from the dealer for less $$ than cheap aftermarket ones at Walmart or parts stores. Same with air and oil filters, quality Delco Gold AGM batteries, and actually ordering tires from the dealer because they will price match on-line prices from places like Tire Rack. Be aware, dealers also sell off brand parts that are less than genuine GM, avoid those if you can. Also, dealers all have different price marks so shop around at various GM dealers and you'll see big price differences on the exact same parts.