A verbal offer is only as good as the paper it's written on.
It's a way some agents have of "fishing" to see if the seller (or seller's agent) thinks an offer might be well-received, and worth writing. A verbal offer is not enforceable, and since it's not written-down, it's often loaded with misunderstandings, since things are not spelled-out.
Let's take for example... your realtor gives a verbal offer to the seller at $500,000. The seller agrees... "go ahead and write it up"... when it's written, they suddenly notice that you've asked for a 200% tax proration, you expect the seller to pay for all the inspections (including termite, mold and radon), the contract is contingent on selling YOUR home first, and they have 180 days to close.
The seller says "if I'd known about all of those other contingencies, I would never have accepted $500,000... so the contract is null and void, OR you can pay $600,000.
Do you see this ending well? Everyone's feelings are hurt, and the deal dies. Always better to put it in writing.