I guess it is a matter of experience.  I would much rather deal with a company like Costco than any small local merchant when it comes to customer satisfaction or resolving disputes.  In most cases I can return a product to Costco with zero hassle or request a price adjustment if they drop the price within a few weeks.  Meanwhile your typical small local merchant is pointing to their all sales are final sign for anything short of a defective product.

That isn't to say small merchants aren't worth patronizing - but simply a matter of fact point that larger companies are usually more willing to incur a financial hit to make the customer happy.