Can anyone help please - buy it now disappeared and someone wants to pay BIN price

[SillyBillyBee]

I have replied to a question regarding payment and they have replied saying do I still have a BIN, in between them sending me the first question and me replying someone has met the reserve and the BIN has gone (its a £40 difference so want to get the BIN)
I've only got a few hours left on this, can anyone advise PLEASE.
TIA

once the item has a bid you'll have to go with the auction, maybe they'll bid too

thats what I thought but I'm not an ebay expert so thought I'd check. Thanks for replying