Here at Shire Silver we make sure that our merchants are serious about accepting precious metals. We do this by requiring for profit businesses to pay us a monthly fee to be listed. This ensures that they don't sign up frivolously or without due consideration. (Non-profit organizations can get free listings.)
We've seen too many sites that list anyone who says "OK", even if its just a clerk that happened to think it was cool when a salesperson or customer stopped by and showed off some silver.