Very interesting and efficient trick to getting a really thorough, truthful critique. Contact someone that knows writing; either reads or writes a lot. Tell them that your friend has this piece that they're trying to get reviews on, and you're helping them out. Share your "friend"'s writing with the person and ask what they think. They should be more open about what they think, as they believe they are not actually talking to the creator. Ask them where they saw any weaknesses, or if they felt the speed was wrong, etc. If they know their stuff, they'll tell you.