I hope you did not accidentally send the seller 1400 TBT and not get it back? That would be horrible.
If the seller does not agree to your 700, I hope to get Ankha in my cycling town soon so you can get her for 500. Cyclers tend to sell 'tier 1' villagers at 500-600 TBT each.
Also, I hope you are aware that your TBT is so highly valuable that a lot of people are offering even up to 6-7 million per 100 TBT.
If you are still having trouble with TBT, please let me know.