When it comes to businesses, you can count on people judging the quality of the business by what they see.  If they come into your place of business and it is cluttered, dirty, disorganized, disheveled, etc. they are going to conclude (and rightfully so) that your business isn't the type of place that puts a high priority on details.  Since the everything (to the customer) revolves around details, they'll go elsewhere.  (NOTE:  The exception to this might be army-navy stores, thrift stores, etc. where people expect a mess.)

The same thing applies to your website.  If they go to your website and it is slow, difficult to navigate, disorganized, has mis-spellings and poor grammar, etc. they're going to assume you're either not competent to find a professional to design your site, or you don't care about details.  Again, most customers will go elsewhere. 

Be aware that the internet is the great equalizer.  When I go to your site I don't know if you're a little guy making candles in your garage, or if you're a big conglomerate with hundreds of thousands of square feet of manufacturing facilities in several countries.  And, frankly, I don't care.  I just want the type of candle I want for the best value.

The old saw, “Cleanliness is next to Godliness,” is true in business.  If you don't care for the tens (maybe hundreds) of thousands of dollars you have invested in your storefront (or shop or whatever) why would I think you're going to care for me.  So in that sense, I really will be “judging your book by its cover.”