You should get him to post prices for the item and maybe a "Or Best Offer". I dont know if hes looking for $75 for the MX-850 he has listed or if hes looking for $200 and the thought of 4-6 emails back and forth will have me searching ebay first.
With a set price people would at least know what hes looking for (ballpark) and have a point to haggle from.
Avid Stamp Collector - I really love 39 Cent Stamps