It is not recommended to buy your skylights from box stores
We have noticed that box stores sell the least expensive skylights. They will try and push the least expensive options even with a quality product like Velux. Also, the employees simply do not have the experience to know what accessories you need such as the correct flashing kit. Recently a customer of ours reported that the “kid” wanted them to buy the self-flashing skylight because it was cheaper. We believe they are trained to say that because the less options you have to choose from the less product you have to stock.