2. “We don’t need to write that down, we have agreed.”

Leave nothing unwritten.  

• Any fact relied on by you must be in the agreement.  Don’t rely on what was agreed informally,  even if it is in writing, but not in the agreement.
• Make sure the agreement records what you mean.  Don’t be shy to insist if the language is not crystal clear.  It should be in plain language and easily understandable.
• The suggested wording in any standard pre-printed form may need to be changed to make it say what you mean.  Juat because it is in a pre-printed document does not mean it cannot be changed.
• You can change the agreement only until it is signed by both parties.  After that the deal is done and you can only change it if the other party agrees and the agreement is changed in writing and signed again by both parties.
• Be careful of simply cancelling the first agreement and signing a new agreement.  It may result in double transfer duty unless done correctly.  Take legal advice.