What is rerolling packs and what is the best way to do it?

I've seen this a few times and wondering what it is?

Basically its when you get a bunch of training and you open a bunch of training packs of whatever promo is out (right now the rolls are Backyard Ballers) and quicksell all the stuff you dont want. Typically people are ”rolling“ for Limiteds but you can roll just to try and profit training. The best way to do it is to go to the prices tab here on mutgg and buy  whatever the highest on the list is (or whatever you can afford) for the listed “target price”. That way if you do end up losing in the long run it wont be as bad since the original training you bought was as cheap as possible. Happy rolling!