I often have Tucson home clients who want to start with verbal offers or counter offers. And that can be fine, though I will add another thought on that later. But I remind my clients that anything we get by phone or email or carrier pigeon for that matter, is meaningless in terms of a legal real estate transaction in Arizona. A proper real estate contract must include all of the terms in writing and bear the signatures of the parties.
And any verbal discussions and agreements between the buyers and sellers either at the home showing, the home inspection or even a chance meeting at Safeway mean...well...diddly unless the issue is reduced to writing in the contract between both parties.
Oh, and that other thought I mentioned earlier on verbal offers and counter offers? I have found that it is quite easy for a party in an offer/counter offer situation to give a quick "NO!" to a verbally offered price or condition. I am a firm believer in putting offers and counter offers in writing for presentation to the other party. That gives the party on the other side a chance to look, think, and talk with their agent before giving a rash answer in what is often an emotional situation for that party.