Turn the offer down.
Go to DOMAIN MANAGEMENT
In your control panel, indicate what your MINIMUM OFFER is (essentially your reserve). This will eliminate any ridiculous low offers.
DO NOT put a figure into the PRICE column. If you do and someone offers you this you this amount you must sell it at that price.
Once an offer comes in that you can accept and live with, then you can TAKE IT TO AUCTION.
If you set it too high, you likely not get offers. If you set it too low, you will be bombarded and bothered by the low ball bids.
The key here is to set a realistic minimum offer, one that you can live with IF no one else were to bid on it.