Flipping: the act of obtaining an item for little to no cost to ones self, and then proceeding to try to sell said item for a profit on NS.
Example A: http://newschoolers.com/web/forums/readthread/thread_id/470605/. I
Example B: http://newschoolers.com/web/forums/readthread/thread_id/470650/.
How Not to Flip
Step 1: If you obtain an item at a very low price, either keep said item, or sell said item for an even lower price.
Step 2: This is not a baseball card collection. Signed items, (refer to example B), are not anymore valuable than an item that is unmarked. In fact, the autograph probably makes said item less valuable.
Step 3: Tramdock, Brociety, Whiskey Militia. If you buy an item off of one of these sites, refer to step 1. No one likes a flipper.