correct, the marketplace will show the join date of the member in the bottom right hand corner. and you can always ask the person for their forum name (if they have it).
that said, posting a fake resale listing is not a terribly common scam as its simply more work/effort/less rewarding than the other scams available out there.
IMO the biggest risk on the resale side for a buyer is the details in the listing being incorrect, but in almost all those cases it was not an intentional mistake vs the person who posted the listing just made a mistake, or truly didnt know what they were selling (in the case of a family member or "not the actual owner").
that said, posting a fake resale listing is not a terribly common scam as its simply more work/effort/less rewarding than the other scams available out there.
IMO the biggest risk on the resale side for a buyer is the details in the listing being incorrect, but in almost all those cases it was not an intentional mistake vs the person who posted the listing just made a mistake, or truly didnt know what they were selling (in the case of a family member or "not the actual owner").