Best answer by Ryan S
If it's not on a sonos.com domain, as in, https://www.sonos.com or https://en.community.sonos.com then it's not likely to be one of ours. I answered the same question here, but I'll leave both up to help spread the word.
This site in particular sparks all of my "scam" hairs, so I'd highly recommend purchasing from a known legitimate vendor.
Edited: forgot an important word....