Yes but anyone with a some sense does a bit more than just call in the first company that offers itself to get a job done. In general good business people will get a feel for the quality (or otherwise) of a service they're being offered. In addition most will have a 'grapevine' of friends and acquaintances who they will ask for advice and recommendations.
The quality of a company's advertising (which is what a web site is) and its other 'visible' facets *does* reflect on that company.