What is online traffic?
Website traffic refers to web users who visit a website. Web traffic is measured in visits, sometimes called "sessions," and is a common way to measure online business effectiveness at attracting an audience.
Is more traffic = more sales?
Not necessarily. More traffic might mean more visits but not all of them might convert. In fact, if you have more traffic and none of them convert (purchase or sign up for something) then you're probably receiving bad traffic.
What do you do about it?
Google Analytics should give you an indication if your bounce rate is too high. By looking at it you should be able to tell you do have bad traffic and study it's source - yes it's possible.
But heads, up generally more traffic, is a good thing but not always. So if someone does decide to "sell you some traffic" then remember not all traffic is equal. you could have just paid traffic for nothing if no one converts.