The easiest way to eliminate this problem for good would be to set the listing up using the Advanced Selling Template, then when you've added the Buy It Now price to the listing select the Best Offer option. Activate the functions to automatically accept offers equal to or above a certain price, as well as setting up the function to automatically reject offers below a certain price. Decide what the minimum amount is that you would be willing to accept, then enter that amount into the "Automatically Accept..." field. Any offers equivalent to, or higher than, that amount will be automatically accepted, at which point the person who submitted the offer will receive an instant confirmation that the offer was accepted and will be prompted to make payment.
Once you've entered an amount in the "Automatically Accept" field enter a price into the "Automatically Reject" field up so that the maximum amount that you would automatically reject is 1p less than the lowest amount that you would automatically accept. By doing this then as a result of not leaving a grey area in between the maximum amount to reject and the minimum amount to accept you would not have to consider offers manually and decide whether to accept, counteroffer or reject the offers. If the Best Offer was high enough then it would automatically be accepted. Should you decide to do that it means less work for you and less chance that you'll miss out on a sale as a result of either not seeing an offer in time or making a mistake with a counteroffer.
