As long as you havae no bids you can revise your item to the price agreed by clicking More Actions to the right of the item.
Let your buyer know when you are doing it and then they bid.
As soon as they bid go to More Actions again and End Item and then End Item to highest bidder
If you have bids then leave it to auction, It is unfair to other bidders.
Most people asking for a BIN price are after a bargain and you may get more in auction