Long time Rock Auto customer here. When I first started using them, they were the best price anywhere for pretty much anything. These days, not so much. I now have to do a lot of comparison shopping, because they are good on some things and high on others. That, coupled with shipping costs makes it hard to justify ordering online sometimes, as my local AutoZone can nearly match the pricing, local sales tax and all...
Out of all of the orders I have ever placed with Rock Auto, they have only ever sent an incorrect part one time, on the current order which I am reviewing. I ordered several different bearings, races, and seals, and one of the bearings, while being marked correctly on the box, contained an incorrect bearing inside. Since it was just one, and the cost of returning it would have been as much as the part cost, I simply ate it and purchased another one locally. Since I'm routinely handed the wrong parts at my local auto parts store, I don't consider this one-time issue to be the norm for Rock Auto, and I will definitely use them again in the future.