I really completely confused here...
Yuitsu, are you upset because a seller is not accepting your best offers? Unfortunately, it is completely up to the seller, and with the recent shipping price changes, this seller may not be able to give you more than a dollar less. As a seller, I get lots of offers all the time (even though I almost never list anything with Best Offer as an option). my acceptance of these offers depends heavily on who the buyer is (as far as if they are a repeat customer, etc.), what they are making an offer on (if they are offering me $1 for a $10 or more item, I simply cannot accept it on the grounds that my family needs to eat), and how many items they are making the offers on.
I suggest maybe communicating more with your seller and in the end if he or she doesn't want to sell to you at certain prices, then maybe you could try looking at the same ponies from other sellers.
In the end, it is really up to the seller. And I know that is hard sometimes, but if you are looking for some kind of deal, you may have to wait for a great auction or a lucky break.
Also, it might be wise not to post the seller's user ID directly here (without having made a transaction yet where money and ponies were exchanged) as he or she could be reading and might be hurt.
No matter what, I wish you the best of luck in collecting and I hope you get what you are after!