Law on Obligation and Contracts

Allan an illegal settler has been living in his house for 10 years. One sunny day, Alvin a millionaire, chanced upon the neighborhood where Allan lives and instantly thought that the place is commercially profitable. Alvin offered to buy Allan's property for a hefty price, but Allan refused. Gun-carrying goons accompanied him when he returned to Allan. This time, Allan could not do any thing but to sign the contract of sale. If Allan went to you for help as his friend. What would you advise him?