Assume you have a home listed for $500,000 and you're getting offers under $475,000. You're countering these offers at $485,000 because you're trying to preserve some profit on the sale. You might be focused on the wrong thing.
Buyers pay mortgage payments, not price. In this case, the buyer may not want to pay more than $2500 PITI for the home (with 20% down at 4.25%, 30 year fixed, 4.32% APR). She is offering a lower price because her payment would be $2589 at $500,000. If you sell to her at her price, you will lose $25,000.
Counter her offer at $500,000 but offer to pay three discount points for her, to lower her rate to 3.75% (4.05% APR). This will bring her payment to $2473. This is actually $10/month lower than what her payment would be, at the no point rate (4.25), for a purchase price of $475,000.
The buyer gets a lower payment and you only "lose " $12,000 instead of $25,000. Your real estate agent will have to understand financing well and "sell" it to the buyer's agent but, if presented properly, everyone gets what they really want.