I think it depends on what you want to buy. If you want to buy wire, you can probably get a better deal from local suppliers due to the shipping costs. However, for other items such as dimmers, ballasts, or breakers, you may find better deals on Amazon. Also, as you probably know, suppliers, both online and local, do not set their prices based on cost plus a fixed markup. Their prices fluctuate depending on various factors such as their inventory, their order period, their business plan, and even the salesperson's mood of the day. SO I think we have to do our homework if we want to get a right price. If I have a continuous flow of jobs such as residentials with high material costs, I would set a competitive price from my local seller. For those in service with a variety of parts in small quantities, online purchases may be more convenient as you can reorder any parts conveniently online as you use it and refill the inventory or in cases easily return it if you don't need it.