Dear Monty: We were selling our home and listed it with a real estate agent we know. We just finished the final touches to show the house, so it goes on the market in a few days. The agent has a customer who looked at it a few days ago. We listed it for $424,900. This customer offered $415k. We said we wanted to put it on the market before we could answer. They returned with a $430k offer and a preapproval letter and will close in 30 days. Is there a relationship with the agent? Has she mispriced the house? We are still determining how to handle it. What should we do?…