So for example you sell someone some bitcoins for Paypal. After 3 days you get a chargeback, as long as you stick an empty envelope with a tracking number in the mail to their physically address within 7 days of the purchase you can still use the tracking number to dispute the chargeback.
If you have a US Paypal account and they also had a US address you should win. I used to do it all the time when I was selling counter-strike CD Keys, used to win every time.
That is really bad advice and stupid to admit publicly. You are committing mail fraud and in most of the bitcoin cases the scammer is not the real owner of the ebay account. So the other scammed party (the ebay account holder) will get an empty envelope and potentially report YOU for it. Doing it once or twice you may get away with it, but if you 'do it all the time' and several people report to the postmaster that you sent them empty envelopes you are going to feel some pain.
If you sell bitcoins on ebay you are going to get hurt. Maybe not all the time but enough to make it not profitable.