seller excepted my first bid in a e-mail.Now they want more money.can they do this?

[swalsh44]

I e-mailed the seller and asked them if they would except my amount bid. They replied yes. That to just make the offer and they would see to it that it would be excepted. Now the seller wants more money for the item. Is the seller able to do this? Do they not have to except my original offer that they excepted?

[reallynicestamps]

If you made a Best Offer through eBay and the seller accepted, he does have to accept (note spelling) the offer.

Best Offers do NOT include shipping. Is that the difference in cost?