Everyone flies different and retains their knowledge differently. I've flown pilots that were rusty and got back to speed in one 2 hour flight while others have taken multiple flights.
Give them study material. I tell all my students to study this before a flight review because it covers a majority of things that every pilot should know -
ASA: Guide to the Flight Review
As for the second guy, you may need to work on stalls, slow flight and ground reference maneuvers (rectangular course) before doing any pattern work with him. Landings are something that a non-proficient pilot will always have trouble with. Before you fly tell the pilot what your expectations are. A majority of pilots know that the flight review is not a pass/fail ride so a lot of them are comfortable knowing that if they don't get a sign off in one flight, it'll take multiple flights. Go to my website and click on the download links tab. I created all the procedures and materials for my students so they can spend more time reviewing the information.
In my experience and opinion, there is no consistent way to evaluate a BFR. Every flight review and every student will be different. If you feel comfortable knowing that the student is not going to violate any regulations or cause any damage to people/property and has demonstrated the abilities of being a safe, proficient and competent pilot, you have done what you can as a CFI to give him/her a sign off for a flight review.