Legal Question in Legal Ethics in California

Probably not. Based on your question it does not appear that you had a binding contract. You promised to pay him an extra $50 if he did not sell the dog before Monday and he promised not to sell the dog until Monday. He broke a promise, but probably did not breach a contract. Likewise, what would have happened if you did not show up on Monday? Would you have been required to buy the dog or pay the $50. No. Obviously, since he sold the dog he is not entitled to anything. If he would have accepted your offer and you agreed to pick the dog up on Monday then he would be in breach. Or if you paid him the $50 up front this would have created an option until Monday and he would have breached that agreement. Either of these two situations may have given you a claim against him. Your mutual promises show that you did not make a firm offer and he did not accept an offer. You only had an agreement that was conditional. Further, even if you did have a legitimate claim your damages are probably minimal (unless the dog was very rare and very expensive). He sold the dog so specific performance is probably not available (i.e. selling you the dog).