Yes, buyer has the right to sell it off to those who can offer a higher price. But as for me, I see according to one's opinion whom I already reserved. If I haven't reserved for anyone, I take high offer ofcourse. But since its already reserved, I can't do that right away. If one going to let it go, then I sell it off to a higher offer. Although he haven't bank in to me, I still need to talk to him about it, so its not like I not going to sell to him unless he offered me >=RM610. 
P/S: If I were to defend myself here, I've already explain to him in PM instead here. It shows that he don't want to spoil my name without stating out my nick the first place. Very nice of him actually.