This is the procedure I typically follow
Step0: Post on thread
Step1: Through PMs, ask seller to show screenshot of Account name + Order history in MTGO (use 2020 order history or previous year with the most transactions) (don't trust their JSP account join date, that doesn't matter)
Step2: Determine who will go first (I typically use the jsp 3/3 rule)
Step3: Get each others in game name
Step4: Begin trade in MTGO *DO NOT MENTION JSP OR FG OR ANYTHING
Step5: Finish trade following who sends/gives first
Please note, asking for purchase history DOES NOT prevent the seller from issuing a charge-back/contacting Wizards saying their acct was hacked/using a hacked mtgo account.
If any of these things happen, Wizards will contact you and ask you how you've obtained your tickets. Saying JSP will cause your account to be closed, so have some story in order, otherwise be prepared for your MTG account to be banned.
Even after following all of these steps, nothing is 99% proof.
Trade carefully.