Make a policy to look at your customer's background / familiarity (i.e if other ppl know this guy ) chances are there will only be a select few that have legit 10 mill + spending budgets.
If your buyer is not a well known server master crafter then you should be obviously cautious.
Ask around if the buyer is known because by now we should know a lot of familiar end game players at mor and lim.
Also if you want to make the extra effort, go and check the MB and see the item's history.
If you see that guy's name show up spending a lot recently on high end gear/ items like HQ i90 gear, rare super expensive housing furniture /pieces ( i.e white raven fragment ).
No way ppl would spend 10-20 mil in an a week or 2 ( not including buying a house ).

If you are selling content then you are selling your safety at the buyer's own consent.
Stranger gil is bad gil.