if you have an interested buyer for these domains, chances are that he's an end user.
The low to mid xx figures are for resellers, and I dont really see resellers trying to buy these domains.
If he's offered you something in the xx range, I would counter with atleast 500, if its in the low xxx range, then I would counter with 750, and if its in the mid xxx range, I would counter with atleast 1300