Signed contract of sale

Hi all, Reaching out to know your thoughts on two things:

1. Is it common practice for real estate agents to get a buyer to sign the contract of sale beforehand while putting in an offer for private sale and then present it to the vendor?
2. Do they send this contract of sale to all interested buyers willing to put in an offer in writing or do they just send it to the one buyer they think are going to lock this property in?

Thank you!