Auto repair facilities in California have to be licensed as such. Performing auto repair service – which can include testing, evaluation, and advice – as a business without said license is a good way to get your tit in a wringer. California’s BAR (Bureau of Automotive Repair) tends to be tough on shops to the point of being overzealous in protecting customers’ interests. It wouldn’t surprise me if parts stores got stung with hefty fines from BAR due to disgruntled customers and decided it wasn’t worth the hassle.