Similar situation happened to me last week, but I was lucky I did not trust it.
I responded to a sellers ad with "PM Sent"
A minute or 2 later I got an email. No PM back, but an email. I did not give my email out in the PM and it was an email address I do not use on LRH. Anyway, email was well written, claimed to be the seller and said "sounds good, pay with Venmo or F&F."
I did not respond to the email. About 5 min later I got a PM from the seller on LRH and a text (I had included my cell number on PM). I called the actual seller and told him of the email. Anyway. me and the "real" seller made the deal and I have gotten a couple more emails from the scammer but I have blocked him.
Just be careful and this is part of the reason I will only deal with well known members, I need to talk with them, and will only send a personal check with "For deposit only" on the back.
Be safe.