Be very careful with a desk review. I would recommend negotiating a full field review at a good fee if you disagree with the appraisal in any way. Don't get into USPAP trouble over a desk review and certainly don't get in more trouble than the person you are reviewing. Don't forget the deadly seven (scope, purpose, intended use/user, etc.).
An enhanced review is the lenders way not to order another appraisal. They are asking you to provide a value conclusion supported with additional comps. Very risky, you will be doing an appraisal and a review. Charge accordingly and be sure to have a complete work file. Good luck.