I've received such offers before and they will let you know, not sure about 50% off the listed price though. I think it depends on the price range. This one below was for a bargain name. I think you can ask if any other of your names received an offer. I accepted the following offer
A prospective buyer has made an offer that is roughly 28% below your asking price for N-a-m-e.com. At the current price, your take-home amount is $XXX. The buyer's offer would make your take-home $XXX.
Please let me know if you'd like to accept the offer, counter or deny.
Trust me guys, BB will surely let you know about any considerable offer and will recommend you what action to take. I did not give any discount for the name below and it sold 2 months after for my asking price. Exactly as BB predicted as well.
A prospective buyer has expressed interest in your domain N-a-m-e.com, but the buyer is seeking a discounted price. We believe that this is a strong domain that could likely reach your asking price if given more time. However, since the name has be listed for a few months, you may want to consider offering a discount in the 5%-10% range.
At the current price, your take-home amount is $XXXX. A 5% discount would reduce your take-home to $XXXX. A 10% discount would reduce your take-home to $XXXX.
Please let me know how you would like to proceed.