Product Owner/Maximizing Value
In terms of PO and maximizing value-should a PO always produce most valuable items first-or would certain items from backlog maybe get into release-like say something not as high priority but very simple that goes along with a high priority item?
The PO maximizes value. This does not mean the PO always picks the most valuable items first: perhaps he can get two slightly less valuable but also less complex items instead.
It really depends on the motivation: does the PO want to add in that simple item just for the sake of doing similar things together, or does the simple item actually have good value for the work it entails?
The PO won't look simply at the value of the items themselves, but will use them to negotiate a valuable Sprint Goal with the Development Team. The items planned into the Sprint Backlog will be a forecast of the corresponding work.
Is the value something you add to a user story ?
When your client is stuck with the idea that everything is important and wanting all at once, how do you guess prioritize your backlog ?
The Development Team should never prioritize the backlog. The PO owns the product backlog, and the Development Team owns the Sprint Backlog, which is composed of items offered by and negotiated with the Product Owner for the upcoming sprint, along with any other items the Development Team feels are needed in order to meet the Sprint Goal.
From the Scrum Guide:
"The Product Owner is the sole person responsible for managing the Product Backlog. Product Backlog management includes: Clearly expressing Product Backlog items; Ordering the items in the Product Backlog to best achieve goals and missions; Optimizing the value of the work the Development Team performs... The Product Owner’s decisions are visible in the content and ordering of the Product Backlog. No one is allowed to tell the Development Team to work from a different set of requirements, and the Development Team isn’t allowed to act on what anyone else says."