Upwork used to offer a one-month free trial of Upwork Plus.
There was talk a while back about them discontinuing the free trial - dunno if they actually followed through on that.
Against this backdrop I can say that scammers of the sort you refer to are not generally paying for a membership.
Of course this is not to say that you can never get scammed by a client paying for a membership.
As an FYI, Plus clients are entitled to 1 free featured job per month, without prejudice to whether they are the actual paid Plus clients or the free trial Plus clients.
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