Anna promises to sell Bert Lot C for $$200,000.$ They agree Bert will transfer $$100,000$ on February $10,2021,$ and $$100,00$ on March $10,2021,$ to Anna to satisfy the payment. They are friends and neighbors, so they discuss the deal casually and never put it in writing.

On February $10,2021,$ Bert transfers $$100,000$ to Anna$$s bank account as they had previously discussed. A couple of days later, Anna calls Bert and tells him that she has another buyer who will pay $$250,000.$

What are Bert's rights?