If you feel comfortable in selling this domain within low-mid $xxx range, and if the ROI (return of investment) is quite high, i would counter-offer $350.
There is a small risk the buyer would change idea, but since the difference between his offer and your counter-offer wouldn't be big, there are many chances he accepts or just offer you something more than the first one ($150).
However, if the ROI is very low, think twice before selling it.