The big problems that the developers face are finance and council approvals which through no fault of theirs can take years and it is a balancing act that they spend the time and the money and by the time they finish the market may have collapsed
From your point of view I would be looking at sunset clause dates and the initial payment.
A couple of grand is nothing in the whole scheme of things, does not even pay for advertising if you have to sell again, it's all about negotiation which they will expect because they are asking you to take it off the market for ? three years with you not having a back door
Remember the agent will not protect you, you have to protect yourself, I am not suggesting that you do anything to ruin what you have because the contract you have may be the only one you will get
But they understand business and they understand negotiation
