Auction question

An item I am interested in says the following:

Exchange Rates:: Any rare materials is worth the average of the buy and sell price from the NPC.

Does this mean, if I am high bidder, that I have to give rare materials, not gold, for the item?

No, it means that you MAY give him materials instead of some or all of the gold (at the rates he mentioned), but you don't have to.

Thank you.