It's rare, but reverse offers do happen. After a Realtor show's my listing I could simply discuss a strategy with my seller & present an offer to the buyers agent. Since it’s the holidays lets pretend the list price of the home is $10,000,000. After the home has shown I type up the offer with my sellers information and an offer of say $9,500,000.00.
The buyer has now been given an offer to consider, and hopefully proceed with. The seller won't sign off on the offer until earnest money has been delivered, parameters have been fully negotiated and of course pre-approval expectations have been met. It's important to understand that there is no one way to conduct a reverse offer. You could offer more attractive terms and conditions then what's considered usually and customary. You could toss in a 90 day closing, furniture, closing cost assistance, golf memberships, a riding lawn mower and much more. The idea is to stimulate interest, even if it's unconventional.
A regular offer is generated by the buyer’s agent to be presented to the seller. In all cases, it’s never a contract until the seller signs it!