Which vendor? What is the graded clarity? Are you buying it loose? Does the vendor have a reasonable return policy?
What does the vendor mean specifically by stating the feather and twisps are not visible... is that from the top at 12"? What about the side view? Whatever their definition, does it match your definition of eyeclean?
All that said, if for example WhiteFlash told me the inclusions are not visible, I would ask if it is eyeclean to my preference (6" from top and sides), and I would trust their response.
Then, yes, if it were me, and assuming it meets my requirements as to (ideal) cut, color, and budget, I'd for sure buy it from B2C and check it out in person in different lighting conditions.