Is there any risk in buying used earbuds and what is the difference between used and refurbished?

benefits:

used earbuds generically have better sound quality than new ones (more controlled and tight bass, less harsh highs and slightly more lush mids) as the longer you use a headphone, the more 'flexible' and 'loosened' the diaphragm (the sound producing membrane of the headphone/earphone) becomes. therefore, the looser diaphragm is capable of moving faster and producing better sounds. this effect is actually called 'burn in' and majority of headphones require 50 hours of 'burn in' to sound optimal.

risks:

used headphones/earbuds may have slightly damaged drivers caused by dust and physical force. they might also be dirty or have chipped and broken parts.