I have personally purchased numerous books from comicmylars. A large chunk of what he sells is consignment, so he has less wiggle room on those prices. But even on those he will work with you with a hundred dollars off here and there. But no, he is not someone you can expect or hope will take a low ball offer.
-J.
I messaged him on ebay to purchase a book in person 2 years back. Piad in cash to knock off the 10% ebay/paypal fee. Seems like a nice guy, but yea he will not really lower the price on his books much.