firs right of refusal

We are trying to buy a house in Massachusetts that currently has an accepted offer with the first right of refusal. The selling agent is trying to get us to sign our P&S before invoking the clause with the first buyers. I thought the clause is invoked when another bid is accepted. How much info should we be given about it- ie how long the other buyers have to waive their right and at which point should it take affect? Plus, I don't feel it's right to sign a P&S before the seller. What are my options?

[HomeGuru]

Those are questions t hat you should ask your real estate agent.