But buying 10 knives at MSRP and selling them for $100 or double what you paid 2 months later is crazy to me, but supply and demand dictates prices and if people are willing to pay it, go for it.
doubling their money 2 months later is an exaggeration and if you do see an extra $100 tacked on it is either a vary rare piece that deserves to have $100 tacked on or it was a very expensive piece in the first place and percentage wise $100 is minimal or average.