Since we're on this topic- would you trade a BNIS Pandemic Legacy for Vanilla Pandemic and the 2 Expansions?
Have you ever played any pandemic before?
My angle would be that you could always buy another Pandemic Legacy later and you could also sell/trade Original pandemic, with expansions. You won't be able to do very much with a used copy of Pandemic Legacy.
So if you have that offer, the safer choice is to trade for something that has a resale value. If you find that you enjoy Pandemic then get Legacy later.