Recently CB has had a influx of scammers sending a PM to members that have posted in S&S.
They offer to sell you the item you said you wanted and provide a email address for contact.
When responding to PM messages please look at the persons profile that sent it.
Typically the scammers are new members that recently joined with zero posts.
The Staff at CB is doing its best to catch them prior to sending the messages.
If you receive a message from someone that you think might be a scammer please use the report feature to report it.

To report a post or a pm look at the bottom left and you will see a triangle with a explanation mark. Hit it.
When the box pops up type the reason you are reporting it and hit send

Edit: The latest WTB scam is a PM indicating a “friend” has what you are looking for, then provide a email address for you to contact the “friend”. If you check, the PM sender will have 0 posts, or threads.